chore: rename remaining subfeed references to siftlode

Replace the leftover 'subfeed' name across logger names + log_config,
frontend localStorage keys, Postgres user/db/volume defaults in the
compose files, .env.example, config.py, backup/restore scripts and the
README. Pure rename; no behavioural change. localStorage keys move from
subfeed.* to siftlode.* (one-time UI-state reset is acceptable).

backend/app/youtube/client.py

@@ -16,7 +16,7 @@ from app.config import settings
 from app.models import User
 from app.security import decrypt
 
-log = logging.getLogger("subfeed.youtube")
+log = logging.getLogger("siftlode.youtube")
 
 GOOGLE_TOKEN_URL = "https://oauth2.googleapis.com/token"
 API_BASE = "https://www.googleapis.com/youtube/v3"