fix(#64): Address PR comments

supabase/migrations/20260110144000_fix_stats_functions_ambiguity.sql

@@ -18,6 +18,7 @@ DECLARE
   v_pokemon_caught BIGINT;
   v_total_users BIGINT;
   v_completed_pokedexes BIGINT;
+  v_updated_at TIMESTAMPTZ := NOW();
 BEGIN
   -- Calculate current stats: count of caught Pokémon
   SELECT COUNT(*) INTO v_pokemon_caught
@@ -39,17 +40,17 @@ BEGIN
   ) completed;
 
   -- Update cache using UPSERT pattern
-  INSERT INTO stats_cache (pokemon_caught, total_users, completed_pokedexes, updated_at)
-  VALUES (v_pokemon_caught, v_total_users, v_completed_pokedexes, NOW())
+  INSERT INTO stats_cache (id, pokemon_caught, total_users, completed_pokedexes, updated_at)
+  VALUES (1, v_pokemon_caught, v_total_users, v_completed_pokedexes, v_updated_at)
   ON CONFLICT (id) DO UPDATE
   SET pokemon_caught = EXCLUDED.pokemon_caught,
       total_users = EXCLUDED.total_users,
       completed_pokedexes = EXCLUDED.completed_pokedexes,
-      updated_at = NOW();
+      updated_at = v_updated_at;
 
   -- Return stats
   RETURN QUERY
-  SELECT v_pokemon_caught, v_total_users, v_completed_pokedexes, NOW() AS updated_at;
+  SELECT v_pokemon_caught, v_total_users, v_completed_pokedexes, v_updated_at AS updated_at;
 END;
 $$;