refactor(config): use dj-database-url for flexible database configuration

- Add dj-database-url package for parsing DATABASE_URL
- Replace hardcoded PostgreSQL config with DATABASE_URL environment variable
- Add connection pooling with conn_max_age and health checks
- Fallback to SQLite for local development when DATABASE_URL is not set
- Remove obsolete production config comments
- Update requirements.txt with new dependency

This change improves deployment flexibility by supporting standard DATABASE_URL format commonly used in cloud platforms (Heroku, Railway, etc.) while maintaining backward compatibility with local development using SQLite.

booking_system/settings.py

@@ -2,6 +2,7 @@ import os
 from pathlib import Path
 from datetime import timedelta
 from dotenv import load_dotenv
+import dj_database_url
 
 load_dotenv()
 
@@ -11,10 +12,8 @@ SECRET_KEY = os.getenv('JWT_SECRET', 'django-insecure-fallback-secret-key')
 
 DEBUG = os.getenv('DEBUG')
 
-# Update ALLOWED_HOSTS for production
 ALLOWED_HOSTS = os.getenv('ALLOWED_HOSTS', '*').split(',')
 
-# Update CORS for production
 CORS_ALLOWED_ORIGINS = os.getenv(
     'CORS_ALLOWED_ORIGINS', 
     'http://localhost:3000,http://127.0.0.1:3000'
@@ -77,23 +76,21 @@ if not DEBUG:
     SECURE_PROXY_SSL_HEADER = ("HTTP_X_FORWARDED_PROTO", "https")
 
 
-# DATABASES = {
-#     'default': {
-#         'ENGINE': 'django.db.backends.sqlite3',
-#         'NAME': BASE_DIR / 'db.sqlite3',
-#     }
-# }
-
-DATABASES = {
-    'default': {
-        'ENGINE': 'django.db.backends.postgresql',
-        'NAME': os.getenv('POSTGRES_DB'),
-        'USER': os.getenv('POSTGRES_USER'),
-        'PASSWORD': os.getenv('POSTGRES_PASSWORD'),
-        'HOST': os.getenv('POSTGRES_HOST', 'postgres'),
-        'PORT': os.getenv('POSTGRES_PORT', 5432),
+if os.getenv('DATABASE_URL'):
+    DATABASES = {
+        'default': dj_database_url.config(
+            default=os.getenv('DATABASE_URL'),
+            conn_max_age=600,
+            conn_health_checks=True,
+        )
+    }
+else:
+    DATABASES = {
+        'default': {
+            'ENGINE': 'django.db.backends.sqlite3',
+            'NAME': BASE_DIR / 'db.sqlite3',
+        }
     }
-}
 
 ENCRYPTION_KEY = os.getenv('ENCRYPTION_KEY')