fix: update last_login timestamp on successful login

The last_login field was never being updated. Now it gets set to the
current UTC timestamp when a user successfully logs in.

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

app/services/auth_service.py

@@ -12,6 +12,7 @@ Note: Customer registration is handled by CustomerService.
 """
 
 import logging
+from datetime import UTC, datetime
 from typing import Any
 
 from sqlalchemy.orm import Session
@@ -59,6 +60,10 @@ class AuthService:
         if not user.is_active:
             raise UserNotActiveException("User account is not active")
 
+        # Update last_login timestamp
+        user.last_login = datetime.now(UTC)
+        db.commit()
+
         token_data = self.auth_manager.create_access_token(user)
 
         logger.info(f"User logged in: {user.username}")