Add isFollowedByCurrentUser field and hasFollowing to feed query

Updated GraphQL operations to support efficient follow status checking:
- Added isFollowedByCurrentUser field to UserSocialsFields fragment
- Removed nested followers array from UserSocialsFields (over-fetching)
- Simplified followUser/unfollowUser mutations to return minimal data
- Added hasFollowing field to GetVideoFeed query for feed mode detection
- Updated getUserFollowingFollowers query to include isFollowedByCurrentUser

These changes enable the mobile app to:
- Display correct follow/unfollow button states without client-side lookups
- Differentiate between "Following" and "Popular" feed modes
- Reduce payload size by removing unnecessary nested data

Backend handles efficient resolution via request-scoped caching.

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

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

src/operations/feed.gql

@@ -19,11 +19,7 @@ fragment UserSocialsFields on UserGQL {
   id
   username
   profileImageUri
-  followers {
-    id
-    username
-    profileImageUri
-  }
+  isFollowedByCurrentUser
 }
 
 fragment VideoCardFields on VideoGQL {
@@ -116,5 +112,6 @@ query GetVideoFeed(
       hasNextPage
       endCursor
     }
+    hasFollowing
   }
 }