fix: add createdAt to login and register responses

- Add createdAt field to register user response
- Add created_at to login SQL query and response
- Fixes "Membre depuis" showing "-" on profile page

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

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

src/controllers/auth.controller.js

@@ -88,6 +88,7 @@ export const register = asyncHandler(async (req, res, next) => {
       firstName: user.first_name,
       lastName: user.last_name,
       role: user.role,
+      createdAt: user.created_at,
     },
   });
 });
@@ -101,7 +102,7 @@ export const login = asyncHandler(async (req, res, next) => {
 
   // Récupérer l'utilisateur
   const result = await pool.query(
-    'SELECT id, email, password, first_name, last_name, role, is_verified, is_active FROM users WHERE email = $1',
+    'SELECT id, email, password, first_name, last_name, role, is_verified, is_active, created_at FROM users WHERE email = $1',
     [email]
   );
 
@@ -137,6 +138,7 @@ export const login = asyncHandler(async (req, res, next) => {
       lastName: user.last_name,
       role: user.role,
       isVerified: user.is_verified,
+      createdAt: user.created_at,
     },
   });
 });