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/middleware/validators.js

@@ -131,6 +131,11 @@ const updateProfileValidation = [
     .isEmail()
     .withMessage('Must be a valid email address')
     .normalizeEmail(),
+  body('wsdcId')
+    .optional()
+    .trim()
+    .matches(/^\d{0,10}$/)
+    .withMessage('WSDC ID must be numeric and up to 10 digits'),
   handleValidationErrors,
 ];