feat: add country and city fields to user profile

- Add country and city fields to User model
- Create database migration for location fields
- Add validation for country and city (max 100 characters)
- Create countries.js with complete list of 195 countries
- Add country dropdown select and city text input to profile page
- Include country and city in GET /api/users/me response
- Update profile form to support location data

Users can now select their country from a dropdown list of all
countries and enter their city name.

backend/src/routes/users.js

@@ -24,6 +24,8 @@ router.get('/me', authenticate, async (req, res, next) => {
         instagramUrl: true,
         facebookUrl: true,
         tiktokUrl: true,
+        country: true,
+        city: true,
         avatar: true,
         createdAt: true,
         updatedAt: true,