Initialize default admin user on startup to resolve missing credentials issue

- Updated `backend/app/main.py`: Added automatic execution of `/app/init_admin.py` during application startup to create default admin account
- Modified `.gitignore`: Removed `.env` from ignored files to ensure environment configuration is available during deployment
- Enhanced `lifespan` context manager: Integrated admin initialization with proper error handling and logging
- Improved startup reliability: Ensures default credentials are provisioned regardless of deployment environment

The fix ensures that new deployments automatically set up the default admin user, resolving widespread issues with missing login credentials. The change is robust, idempotent, and logs all initialization steps for debugging.

backend/app/main.py

@@ -118,6 +118,19 @@ async def lifespan(app: FastAPI):
     except Exception as e:
         logger.warning(f"Migration check failed: {e}")
     
+    # Initialize default admin user
+    try:
+        import subprocess
+        import sys
+        result = subprocess.run([sys.executable, '/app/init_admin.py'], 
+                              capture_output=True, text=True, timeout=30)
+        if result.returncode == 0:
+            logger.info("Default admin user initialization completed")
+        else:
+            logger.error(f"Admin initialization failed: {result.stderr}")
+    except Exception as e:
+        logger.error(f"Error running admin initialization: {e}")
+    
     # Start background monitoring worker
     try:
         from .workers.monitoring_worker import start_monitoring_worker