feat: Add timezone setting in preferences + clickable logo

- Add timezone dropdown to settings modal with common timezones
- Save/load timezone preference per user
- Apply user's timezone preference after authentication
- Override system default with user preference if set
- Make dashboard logo clickable (returns to default filters)
- Show current timezone in settings

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

index.php

@@ -36,6 +36,21 @@ if (!str_starts_with($requestPath, '/api/')) {
 
     // Initialize audit log model
     $GLOBALS['auditLog'] = new AuditLogModel($conn);
+
+    // Check if user has a timezone preference and apply it
+    if ($currentUser && isset($currentUser['user_id'])) {
+        require_once 'models/UserPreferencesModel.php';
+        $prefsModel = new UserPreferencesModel($conn);
+        $userTimezone = $prefsModel->getPreference($currentUser['user_id'], 'timezone', null);
+        if ($userTimezone) {
+            // Override system timezone with user preference
+            date_default_timezone_set($userTimezone);
+            $GLOBALS['config']['TIMEZONE'] = $userTimezone;
+            $now = new DateTime('now', new DateTimeZone($userTimezone));
+            $GLOBALS['config']['TIMEZONE_OFFSET'] = $now->getOffset() / 60;
+            $GLOBALS['config']['TIMEZONE_ABBREV'] = $now->format('T');
+        }
+    }
 }
 
 // Simple router