refactor: Umstellung auf Mini-MVC-Architektur (Issue #46)

- Front Controller Pattern mit public/index.php als Einstiegspunkt
- Eigenes Routing (App\Core\Router) ohne externes Framework
- Controller: HomeController, ImpressumController, DatenschutzController
- Views mit gemeinsamem Layout (app/views/layouts/main.php)
- PSR-4 Autoloading
- Statische Assets nach public/ verschoben
- Alte Dateien (index.php, impressum.html, datenschutz.html) geloescht
- 301-Redirects fuer alte URLs
- PHP 8.5 kompatibel
- Apache DocumentRoot auf public/ gesetzt

public/index.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Front Controller – Single Entry Point
+ * All requests are routed through this file.
+ */
+
+// Autoloader (PSR-4 style, simple)
+spl_autoload_register(function (string $class): void {
+    $prefix = 'App\\';
+    $baseDir = __DIR__ . '/../app/';
+
+    $len = strlen($prefix);
+    if (strncmp($prefix, $class, $len) !== 0) {
+        return;
+    }
+
+    $relativeClass = substr($class, $len);
+    // Lowercase directory names, keep class name case
+    $parts = explode('\\', $relativeClass);
+    $className = array_pop($parts);
+    $parts = array_map('strtolower', $parts);
+    $parts[] = $className;
+    $file = $baseDir . implode('/', $parts) . '.php';
+
+    if (file_exists($file)) {
+        require $file;
+    }
+});
+
+use App\Core\Router;
+
+$router = new Router();
+
+// Define routes
+$router->addRoute('/', \App\Controllers\HomeController::class, 'index');
+$router->addRoute('/impressum', \App\Controllers\ImpressumController::class, 'index');
+$router->addRoute('/datenschutz', \App\Controllers\DatenschutzController::class, 'index');
+
+// Dispatch
+$uri = $_SERVER['REQUEST_URI'] ?? '/';
+$router->dispatch($uri);