feat: Add auth handoff mutation operations

Adds GraphQL operations for:
- CreateAuthHandoffToken: Get handoff token for mobile-to-web auth
- ExchangeAuthHandoffToken: Exchange token for Firebase custom token

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

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

src/operations/payments.gql

@@ -63,3 +63,17 @@ mutation CancelSubscription {
     stripeSubscriptionId
   }
 }
+
+mutation CreateAuthHandoffToken {
+  createAuthHandoffToken {
+    token
+    expiresInSeconds
+  }
+}
+
+mutation ExchangeAuthHandoffToken($token: String!) {
+  exchangeAuthHandoffToken(token: $token) {
+    customToken
+    userId
+  }
+}

src/operations/video.gql

@@ -211,13 +211,6 @@ query GetMedianRunForVideo($videoId: Int!) {
   }
 }
 
-query GetAverageDifficultyForVideo($videoId: Int!) {
-  getVideo(videoId: $videoId) {
-    id
-    averageDifficulty
-  }
-}
-
 fragment StreamWithEndFrames on UploadStreamGQL {
   id
   streamSegmentType

src/schema.gql

@@ -1072,6 +1072,13 @@ type Mutation {
   deleteUser: Boolean!
   createSubscription(priceId: String!): CreateSubscriptionResultGQL!
   cancelSubscription: UserSubscriptionStatusGQL!
+  submitCancellationFeedback(
+    reasons: [CancellationReasonEnum!] = null
+    feedback: String = null
+    metadata: CancellationFeedbackMetadataInput = null
+  ): Boolean!
+  createAuthHandoffToken: AuthHandoffTokenGQL!
+  exchangeAuthHandoffToken(token: String!): ExchangeAuthHandoffResultGQL!
   findPrerecordTableLayout(b64Image: String!, videoId: Int!): HomographyInfoGQL
   createUploadStream(
     videoMetadata: VideoMetadataInput!
@@ -1196,6 +1203,31 @@ type CreateSubscriptionResultGQL {
   sessionId: String!
 }
 
+enum CancellationReasonEnum {
+  DONT_PLAY_ENOUGH
+  TOO_EXPENSIVE
+  MISSING_FEATURES
+  TECHNICAL_ISSUES
+  DATA_NOT_ACCURATE
+  OTHER
+}
+
+input CancellationFeedbackMetadataInput {
+  appVersion: String = null
+  gitRevision: String = null
+  platform: String = null
+}
+
+type AuthHandoffTokenGQL {
+  token: String!
+  expiresInSeconds: Int!
+}
+
+type ExchangeAuthHandoffResultGQL {
+  customToken: String!
+  userId: Int!
+}
+
 type CreateUploadStreamReturn {
   videoId: Int!
 }