fix: resolve TypeScript build errors from leftJoin nullable types

Non-null assert photo/achievement ids that are structurally non-null
due to FK constraints but nullable in Drizzle's leftJoin return type.
Add missing description field to enrichVideo model select and map.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/backend/src/graphql/resolvers/videos.ts

@@ -41,6 +41,7 @@ async function enrichVideo(db: DB, video: typeof videos.$inferSelect) {
       artist_name: users.artist_name,
       slug: users.slug,
       avatar: users.avatar,
+      description: users.description,
     })
     .from(video_models)
     .leftJoin(users, eq(video_models.user_id, users.id))
@@ -63,9 +64,19 @@ async function enrichVideo(db: DB, video: typeof videos.$inferSelect) {
     .from(video_plays)
     .where(eq(video_plays.video_id, video.id));
 
+  const models = modelRows
+    .filter((m) => m.id !== null)
+    .map((m) => ({
+      id: m.id!,
+      artist_name: m.artist_name,
+      slug: m.slug,
+      avatar: m.avatar,
+      description: m.description,
+    }));
+
   return {
     ...video,
-    models: modelRows,
+    models,
     movie_file: movieFile,
     likes_count: likesCount[0]?.count || 0,
     plays_count: playsCount[0]?.count || 0,