fix: Include timezone in /me endpoint response for persistence

The getUserById method (called by /me endpoint) was missing the timezone
field in its response, causing timezone preferences to revert to UTC after
page refresh. This fix ensures the timezone is returned alongside other
user profile data.

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

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

maternal-app/maternal-app-backend/src/modules/auth/auth.service.ts

@@ -363,6 +363,7 @@ export class AuthService {
         name: user.name,
         role: 'user',
         locale: user.locale,
+        timezone: user.timezone,
         emailVerified: user.emailVerified,
         preferences: user.preferences,
         families,