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/models.ts

@@ -15,8 +15,8 @@ async function enrichModel(db: DB, user: typeof users.$inferSelect) {
 
   const seen = new Set<string>();
   const photos = photoRows
-    .filter((p) => p.id && !seen.has(p.id) && seen.add(p.id))
-    .map((p) => ({ id: p.id, filename: p.filename }));
+    .filter((p) => p.id !== null && !seen.has(p.id!) && seen.add(p.id!))
+    .map((p) => ({ id: p.id!, filename: p.filename! }));
 
   return { ...user, photos };
 }