fix: set Africa/Douala as default timezone fallback

This resolves the "date_default_timezone_set(): Timezone ID '' is invalid" error that occurs when APP_TIMEZONE environment variable is not properly set in deployment environments like Dokploy.

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

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

Author: mckenziearts

config/app.php

@@ -67,7 +67,7 @@
     |
     */
 
-    'timezone' => env('APP_TIMEZONE', 'UTC'),
+    'timezone' => env('APP_TIMEZONE', 'Africa/Douala'),
 
     /*
     |--------------------------------------------------------------------------