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).

frontend/src/lib/notifications.ts

@@ -71,8 +71,8 @@ export interface NotifyInput {
   transient?: boolean; // live status: sticky toast, not persisted (see Notification.transient)
 }
 
-const HISTORY_KEY = "subfeed.notifications";
-const SETTINGS_KEY = "subfeed.notifSettings";
+const HISTORY_KEY = "siftlode.notifications";
+const SETTINGS_KEY = "siftlode.notifSettings";
 const MAX_HISTORY = 100;
 const ERROR_TTL = 15000;