feat(userbot,api,frontend): backfill stories and unbreak all-stories list

backend/src/userbot/modules/stories/repository.py

@@ -22,6 +22,20 @@ ON CONFLICT (account_id, peer_id, story_id) DO UPDATE SET
 """
 
 
+async def is_downloaded(
+    pool: asyncpg.Pool, account_id: int, peer_id: int, story_id: int
+) -> bool:
+    return bool(
+        await pool.fetchval(
+            "SELECT downloaded FROM stories "
+            "WHERE account_id = $1 AND peer_id = $2 AND story_id = $3",
+            account_id,
+            peer_id,
+            story_id,
+        )
+    )
+
+
 async def upsert_story(  # noqa: PLR0913
     pool: asyncpg.Pool,
     account_id: int,