Enhance security and configuration of contact form: Added Content Security Policy and Strict-Transport-Security headers in .htaccess for improved security. Updated error handling to use a single 404.php for various error codes. Removed deprecated config.php and composer.json files, and implemented IP address detection for better security. Added honeypot field for bot protection in contact form and improved session security settings in functions.php.

public/404.php

@@ -0,0 +1,73 @@
+<?php
+require_once 'includes/functions.php';
+
+// Page configuration
+$page_title = '404 - Seite nicht gefunden | HexaHost.de';
+$page_description = 'Die angeforderte Seite wurde nicht gefunden.';
+$current_page = '404';
+
+// Set 404 header
+http_response_code(404);
+
+// Include header
+includeHeader($page_title, $page_description, $current_page);
+?>
+
+<main>
+    <section class="error-page">
+        <div class="container">
+            <div class="error-content glass-card">
+                <div class="error-code">404</div>
+                <h1>Seite nicht gefunden</h1>
+                <p>Die angeforderte Seite existiert leider nicht oder wurde verschoben.</p>
+                <div class="error-actions">
+                    <a href="index.php" class="btn btn-primary">Zur Startseite</a>
+                    <a href="contact.php" class="btn btn-secondary">Kontakt aufnehmen</a>
+                </div>
+            </div>
+        </div>
+    </section>
+</main>
+
+<style>
+.error-page {
+    min-height: 60vh;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    padding: 4rem 0;
+}
+.error-content {
+    text-align: center;
+    padding: 3rem;
+    max-width: 500px;
+}
+.error-code {
+    font-size: 6rem;
+    font-weight: 700;
+    background: linear-gradient(135deg, #ff51f9, #a348ff);
+    -webkit-background-clip: text;
+    -webkit-text-fill-color: transparent;
+    background-clip: text;
+    line-height: 1;
+    margin-bottom: 1rem;
+}
+.error-content h1 {
+    font-size: 1.75rem;
+    margin-bottom: 1rem;
+}
+.error-content p {
+    color: #888;
+    margin-bottom: 2rem;
+}
+.error-actions {
+    display: flex;
+    gap: 1rem;
+    justify-content: center;
+    flex-wrap: wrap;
+}
+</style>
+
+<?php
+includeFooter();
+?>