Add PHPUnit tests and update UI

- Add PHPUnit 11.0 testing framework
- Create unit tests for Database and Crawler classes
- Create integration tests for Crawler
- Add phpunit.xml configuration
- Change UI background color to rose
- All 9 tests passing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

phpunit.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/11.0/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         colors="true"
+         cacheDirectory=".phpunit.cache"
+         testdox="true">
+    <testsuites>
+        <testsuite name="Unit Tests">
+            <directory>tests/Unit</directory>
+        </testsuite>
+        <testsuite name="Integration Tests">
+            <directory>tests/Integration</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory>src/classes</directory>
+        </include>
+    </source>
+</phpunit>