Add roadmap management, service worker, and user invitation features

- Implemented roadmap.php for managing roadmap items with filtering options by quarter and status.
- Added a service worker (sw.js) to handle push notifications and click events for calendar appointments.
- Created users.php for admin to manage team members and invitations, including user creation and deletion functionalities.

api/theme.php

@@ -0,0 +1,48 @@
+<?php
+/**
+ * Fociz Thema API Endpoint (Dark / Light / System)
+ */
+
+header('Content-Type: application/json; charset=utf-8');
+require_once __DIR__ . '/../includes/auth.php';
+
+$user = require_auth(true);
+$userId = (int)$user['id'];
+
+if ($_SERVER['REQUEST_METHOD'] === 'GET') {
+    $currentTheme = get_user_theme($userId);
+    echo json_encode([
+        'success' => true,
+        'theme'   => $currentTheme,
+    ]);
+    exit;
+}
+
+if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+    $raw = file_get_contents('php://input');
+    $data = json_decode($raw, true);
+    
+    $theme = $data['theme'] ?? ($_POST['theme'] ?? 'dark');
+    if (!in_array($theme, ['dark', 'light', 'system'])) {
+        http_response_code(400);
+        echo json_encode(['success' => false, 'error' => 'Ongeldig thema. Kies dark, light of system.']);
+        exit;
+    }
+
+    $ok = update_user_theme($userId, $theme);
+    if ($ok) {
+        echo json_encode([
+            'success' => true,
+            'theme'   => $theme,
+            'message' => 'Themavoorkeur succesvol opgeslagen.',
+        ]);
+    } else {
+        http_response_code(500);
+        echo json_encode(['success' => false, 'error' => 'Kon thema niet opslaan in database.']);
+    }
+    exit;
+}
+
+http_response_code(405);
+echo json_encode(['success' => false, 'error' => 'Method not allowed']);
+