perf(*): bound list queries, batch fetches, harden media downloads

backend/src/utils/read/peers.py

@@ -42,7 +42,8 @@ async def get_peer_history(
     rows = await pool.fetch(
         "SELECT observed_at, first_name, last_name, username, phone, "
         "photo_unique_id, is_deleted_account FROM peer_history "
-        "WHERE account_id = $1 AND peer_id = $2 ORDER BY observed_at DESC",
+        "WHERE account_id = $1 AND peer_id = $2 "
+        "ORDER BY observed_at DESC LIMIT 500",
         account_id,
         peer_id,
     )