feat(cache): implement centralized caching layer for improved performance and reduced API calls

feat(microsoft-integration): enhance inbox and events fetching with caching support
feat(auth): include theme and notification settings in user data retrieval
feat(profile): improve password visibility toggle functionality
feat(planner): optimize event synchronization with Outlook using caching
fix(notifications): update mail badge handling for mobile and desktop

mail.php

@@ -11,8 +11,9 @@ require_once __DIR__ . '/includes/integrations/microsoft.php';
 $userId = (int)($currentUser['id'] ?? 0);
 $db = get_db_connection();
 
-// Haal initiële inbox data op
-$inboxData = microsoft_fetch_inbox_messages($userId, 30);
+// Haal initiële inbox data op (met 45s cache, tenzij ?refresh=1)
+$forceRefresh = !empty($_GET['refresh']) && $_GET['refresh'] === '1';
+$inboxData = microsoft_fetch_inbox_messages($userId, 30, false, $forceRefresh);
 $messages = $inboxData['messages'] ?? [];
 $isDemo = !empty($inboxData['is_demo']);
 $unreadCount = (int)($inboxData['unread_count'] ?? 0);
@@ -720,7 +721,7 @@ async function refreshMailbox() {
     if (icon) icon.classList.add('animate-spin');
 
     try {
-        const res = await fetch('/api/mail.php?action=get_inbox');
+        const res = await fetch('/api/mail.php?action=get_inbox&refresh=1');
         const data = await res.json();
         if (data.success && data.messages) {
             allMessages = data.messages;