feat(contact): server-side PHP mail handler for contact form

Fix #34: E-Mail-Versand via PHP

- PHP POST handler with server-side validation (name, email, message)
- mail() with From/Reply-To set to form email address
- Recipient: mki@kies-media.de
- Honeypot spam protection (hidden field)
- Minimum submit time check (3 seconds)
- Session-based rate limiting (60s between submissions)
- Header injection protection
- Error messages displayed above form
- Success message after successful send
- Form values preserved on validation errors
- Removed client-side mailto: JavaScript logic
- Added CSS for error display and honeypot hiding

css/haus-schleusingen.css

@@ -991,6 +991,36 @@ nav.scrolled .nav-hamburger span::after {
   transform: translateY(-1px);
 }
 
+.form-errors {
+  background: #fdf2f2;
+  border: 1px solid #e8a0a0;
+  padding: 1rem 1.2rem;
+  margin-bottom: 1.2rem;
+}
+
+.form-errors ul {
+  margin: 0;
+  padding: 0 0 0 1.2rem;
+  list-style: disc;
+}
+
+.form-errors li {
+  font-size: 0.85rem;
+  color: #9e2c2c;
+  line-height: 1.6;
+}
+
+.hp-field {
+  position: absolute;
+  left: -9999px;
+  top: -9999px;
+  width: 0;
+  height: 0;
+  overflow: hidden;
+  opacity: 0;
+  pointer-events: none;
+}
+
 .form-success {
   display: none;
   text-align: center;

index.php

@@ -1,3 +1,104 @@
+<?php
+session_start();
+
+// --- Helper functions ---
+function normalizeContactValue(string $value): string
+{
+    return trim($value);
+}
+
+function escapeContactValue(string $value): string
+{
+    return htmlspecialchars($value, ENT_QUOTES, 'UTF-8');
+}
+
+function containsHeaderInjection(string $value): bool
+{
+    return (bool) preg_match('/[\r\n]/', $value);
+}
+
+// --- Form processing ---
+$formErrors = [];
+$formSuccess = false;
+$formData = ['fname' => '', 'lname' => '', 'email' => '', 'phone' => '', 'interest' => 'Besichtigung anfragen', 'message' => ''];
+
+if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+    // Collect and normalize input
+    $formData['fname']    = normalizeContactValue((string) ($_POST['fname'] ?? ''));
+    $formData['lname']    = normalizeContactValue((string) ($_POST['lname'] ?? ''));
+    $formData['email']    = normalizeContactValue((string) ($_POST['email'] ?? ''));
+    $formData['phone']    = normalizeContactValue((string) ($_POST['phone'] ?? ''));
+    $formData['interest'] = normalizeContactValue((string) ($_POST['interest'] ?? ''));
+    $formData['message']  = normalizeContactValue((string) ($_POST['message'] ?? ''));
+
+    // Honeypot check – hidden field must be empty
+    $honeypot = normalizeContactValue((string) ($_POST['website'] ?? ''));
+    if ($honeypot !== '') {
+        // Bot detected – pretend success
+        $formSuccess = true;
+        $formData = ['fname' => '', 'lname' => '', 'email' => '', 'phone' => '', 'interest' => 'Besichtigung anfragen', 'message' => ''];
+    } else {
+        // Server-side validation
+        if ($formData['fname'] === '') {
+            $formErrors[] = 'Bitte geben Sie Ihren Vornamen an.';
+        }
+        if ($formData['lname'] === '') {
+            $formErrors[] = 'Bitte geben Sie Ihren Nachnamen an.';
+        }
+        if ($formData['email'] === '' || !filter_var($formData['email'], FILTER_VALIDATE_EMAIL)) {
+            $formErrors[] = 'Bitte geben Sie eine gültige E-Mail-Adresse an.';
+        }
+        if ($formData['message'] === '') {
+            $formErrors[] = 'Bitte geben Sie eine Nachricht ein.';
+        }
+
+        // Header injection check
+        if (containsHeaderInjection($formData['email']) || containsHeaderInjection($formData['fname'] . ' ' . $formData['lname'])) {
+            $formErrors[] = 'Ungültige Zeichen in den Eingabefeldern.';
+        }
+
+        // Minimum time check – form submitted too fast (< 3 seconds)
+        $formTime = isset($_POST['form_time']) ? (int) $_POST['form_time'] : 0;
+        if ($formTime > 0 && (time() - $formTime) < 3) {
+            $formErrors[] = 'Das Formular wurde zu schnell abgeschickt. Bitte versuchen Sie es erneut.';
+        }
+
+        // Session rate limit – max 1 submission per 60 seconds
+        $lastSubmit = $_SESSION['last_contact_submit'] ?? 0;
+        if ($lastSubmit && (time() - $lastSubmit) < 60) {
+            $formErrors[] = 'Bitte warten Sie einen Moment vor der nächsten Anfrage.';
+        }
+
+        // Send email if no errors
+        if (empty($formErrors)) {
+            $to      = 'mki@kies-media.de';
+            $subject = 'Kontaktanfrage: ' . $formData['interest'];
+            $body    = "Von: {$formData['fname']} {$formData['lname']}\n"
+                     . "E-Mail: {$formData['email']}\n";
+            if ($formData['phone'] !== '') {
+                $body .= "Telefon: {$formData['phone']}\n";
+            }
+            $body .= "Anliegen: {$formData['interest']}\n\n"
+                     . $formData['message'];
+
+            $headers  = "From: {$formData['email']}\r\n";
+            $headers .= "Reply-To: {$formData['email']}\r\n";
+            $headers .= "Content-Type: text/plain; charset=UTF-8\r\n";
+            $headers .= "X-Mailer: PHP/" . phpversion();
+
+            $mailSent = mail($to, $subject, $body, $headers);
+
+            if ($mailSent) {
+                $formSuccess = true;
+                $_SESSION['last_contact_submit'] = time();
+                $formData = ['fname' => '', 'lname' => '', 'email' => '', 'phone' => '', 'interest' => 'Besichtigung anfragen', 'message' => ''];
+            } else {
+                $formErrors[] = 'Leider konnte die E-Mail nicht gesendet werden. Bitte versuchen Sie es später erneut oder schreiben Sie uns direkt an mki@kies-media.de.';
+            }
+        }
+    }
+}
+?>
 <!doctype html>
 <html lang="de">
   <head>
@@ -531,15 +632,31 @@
           paar Terminvorschläge an.
         </p>
         <div class="contact-form">
-          <form id="contactForm">
+<?php if ($formSuccess): ?>
+          <div class="form-success" style="display: block">
+            <p>Vielen Dank für Ihre Anfrage!</p>
+            <br />
+            <small>Wir haben Ihre Nachricht erhalten und melden uns innerhalb von 24 Stunden bei Ihnen.</small>
+          </div>
+<?php else: ?>
+<?php if (!empty($formErrors)): ?>
+          <div class="form-errors">
+            <ul>
+<?php foreach ($formErrors as $error): ?>
+              <li><?= escapeContactValue($error) ?></li>
+<?php endforeach; ?>
+            </ul>
+          </div>
+<?php endif; ?>
+          <form id="contactForm" method="post">
             <div class="form-row">
               <div class="form-field">
                 <label for="fname">Vorname</label>
-                <input type="text" id="fname" name="fname" placeholder="Max" required />
+                <input type="text" id="fname" name="fname" placeholder="Max" required value="<?= escapeContactValue($formData['fname']) ?>" />
               </div>
               <div class="form-field">
                 <label for="lname">Nachname</label>
-                <input type="text" id="lname" name="lname" placeholder="Mustermann" required />
+                <input type="text" id="lname" name="lname" placeholder="Mustermann" required value="<?= escapeContactValue($formData['lname']) ?>" />
               </div>
             </div>
             <div class="form-row">
@@ -551,20 +668,25 @@
                   name="email"
                   placeholder="max@beispiel.de"
                   required
+                  value="<?= escapeContactValue($formData['email']) ?>"
                 />
               </div>
               <div class="form-field">
                 <label for="phone">Telefon</label>
-                <input type="tel" id="phone" name="phone" placeholder="+49 ..." />
+                <input type="tel" id="phone" name="phone" placeholder="+49 ..." value="<?= escapeContactValue($formData['phone']) ?>" />
               </div>
             </div>
             <div class="form-row">
               <div class="form-field full">
                 <label for="interest">Anliegen</label>
                 <select id="interest" name="interest">
-                  <option>Besichtigung anfragen</option>
-                  <option>Allgemeine Informationen</option>
-                  <option>Mietbewerbung einreichen</option>
+<?php
+$interestOptions = ['Besichtigung anfragen', 'Allgemeine Informationen', 'Mietbewerbung einreichen'];
+foreach ($interestOptions as $opt):
+    $selected = ($formData['interest'] === $opt) ? ' selected' : '';
+?>
+                  <option<?= $selected ?>><?= escapeContactValue($opt) ?></option>
+<?php endforeach; ?>
                 </select>
               </div>
             </div>
@@ -576,16 +698,20 @@
                   name="message"
                   rows="4"
                   placeholder="Ihre Nachricht ..."
-                ></textarea>
+                  required
+                ><?= escapeContactValue($formData['message']) ?></textarea>
               </div>
             </div>
+            <!-- Honeypot: hidden field for spam bots -->
+            <div class="hp-field" aria-hidden="true">
+              <label for="website">Website</label>
+              <input type="text" id="website" name="website" tabindex="-1" autocomplete="off" />
+            </div>
+            <!-- Form load timestamp for minimum-submit-time check -->
+            <input type="hidden" name="form_time" value="<?= time() ?>" />
             <button type="submit" class="btn-submit">Anfrage absenden</button>
           </form>
-          <div class="form-success" id="formSuccess">
-            <p>Vielen Dank für Ihre Anfrage!</p>
-            <br />
-            <small>Ihr E-Mail-Programm wurde geöffnet. Bitte senden Sie die E-Mail ab, damit Ihre Anfrage bei uns eingeht.</small>
-          </div>
+<?php endif; ?>
         </div>
         <div class="contact-details">
           <p>Oder schreiben Sie uns direkt: <a href="mailto:mki@kies-media.de">mki@kies-media.de</a></p>

js/haus-schleusingen.js

@@ -71,35 +71,7 @@ $(function () {
     }
   });
 
-  // Form submit – opens email client with pre-filled mailto: link
-  $("#contactForm").on("submit", function (e) {
-    e.preventDefault();
-
-    var fname = $("#fname").val().trim();
-    var lname = $("#lname").val().trim();
-    var email = $("#email").val().trim();
-    var phone = $("#phone").val().trim();
-    var interest = $("#interest").val();
-    var message = $("#message").val().trim();
-
-    var subject = "Kontaktanfrage: " + interest;
-    var body = "Von: " + fname + " " + lname + "\n";
-    body += "E-Mail: " + email + "\n";
-    if (phone) body += "Telefon: " + phone + "\n";
-    body += "Anliegen: " + interest + "\n\n";
-    body += message;
-
-    var mailto =
-      "mailto:mki@kies-media.de" +
-      "?subject=" + encodeURIComponent(subject) +
-      "&body=" + encodeURIComponent(body);
-
-    window.location.href = mailto;
-
-    // Show success message
-    $("#contactForm").hide();
-    $("#formSuccess").fadeIn(400);
-  });
+  // Form submit is handled server-side by PHP – no JS intervention needed.
 });
 
 // Mobile hamburger menu (vanilla JS)