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/sync/runner.py

@@ -12,7 +12,7 @@ from sqlalchemy.orm import Session
 
 from app import progress, quota, sysconfig
 
-log = logging.getLogger("subfeed.sync")
+log = logging.getLogger("siftlode.sync")
 from app.models import Channel, OAuthToken, Subscription, User
 from app.sync.subscriptions import import_subscriptions
 from app.sync.videos import (