Refactor database handling to require PostgreSQL connection, removing fallback to JSON. Implement error handling for database unavailability in key files. Update .env.example to reflect mandatory DATABASE_URL for local development. Remove Firebase configuration and related code from the project.

config.php

@@ -34,15 +34,8 @@ function load_env() {
 // Automatically load on include
 load_env();
 
-function get_firebase_config(): array {
-    return [
-        'apiKey'            => getenv('FIREBASE_API_KEY') ?: '',
-        'authDomain'        => getenv('FIREBASE_AUTH_DOMAIN') ?: '',
-        'projectId'         => getenv('FIREBASE_PROJECT_ID') ?: '',
-        'storageBucket'     => getenv('FIREBASE_STORAGE_BUCKET') ?: '',
-        'messagingSenderId' => getenv('FIREBASE_MESSAGING_SENDER_ID') ?: '',
-        'appId'             => getenv('FIREBASE_APP_ID') ?: '',
-    ];
+class DatabaseUnavailableException extends RuntimeException
+{
 }
 
 /**