Add lastSegmentUploadedAt to UploadStreamGQL

Surfaces the timestamp of the most recently uploaded chunk so clients can tell
an actively-uploading stream from a partially-uploaded, stalled/paused one
(combined with isCompleted).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/index.tsx

@@ -3541,6 +3541,7 @@ export type UploadStreamGql = {
   initPlaylistUploadStatus?: Maybe<InitPlaylistUploadStatusEnum>;
   isCompleted: Scalars["Boolean"]["output"];
   lastIntendedSegmentBound?: Maybe<Scalars["Int"]["output"]>;
+  lastSegmentUploadedAt?: Maybe<Scalars["DateTime"]["output"]>;
   linksRequested: Scalars["Int"]["output"];
   lowestUnuploadedSegmentIndex: Scalars["Int"]["output"];
   resolution: VideoResolutionGql;

src/schema.gql

@@ -530,6 +530,7 @@ type UploadStreamGQL {
   initPlaylistUploadStatus: InitPlaylistUploadStatusEnum
   lowestUnuploadedSegmentIndex: Int!
   uploadCompletionCursor: Int!
+  lastSegmentUploadedAt: DateTime
   errors: [StreamErrorGQL!]!
   createdAt: DateTime!
   updatedAt: DateTime!