fix: profile page form pre-population and WSDC ID editing

- Add useEffect to pre-fill profile form with current user data
- Add WSDC ID field to profile edit form with numeric validation
- Update backend to accept wsdcId in profile updates with null handling
- Add wsdcId validation to updateProfileValidation middleware
- Include firstName, lastName, wsdcId in GET /api/users/me response

Fixes issue where profile inputs were empty on page load and allows
users to update their WSDC ID.

backend/src/routes/users.js

@@ -17,6 +17,9 @@ router.get('/me', authenticate, async (req, res, next) => {
         username: true,
         email: true,
         emailVerified: true,
+        firstName: true,
+        lastName: true,
+        wsdcId: true,
         avatar: true,
         createdAt: true,
         updatedAt: true,