feat(notification): add persistent notification

example.env

@@ -406,6 +406,17 @@ DATABASE_URL=postgres://postgres:postgres@localhost:5432/oxicloud
 #OXICLOUD_GRANT_CLEANUP_GRACE_DAYS=15
 #OXICLOUD_GRANT_CLEANUP_INTERVAL_HOURS=24
 
+# ─── Persistent notifications (bell) ─────────────────────────────
+# Retention window (in days) for READ notifications in the bell.
+# Unread rows are preserved unconditionally — that's the point of
+# the durable table: a user offline for a month still sees the
+# share-granted notice on next login. The `notifications_cleanup`
+# scheduled job runs daily and deletes read rows older than this.
+#
+# Minimum 1 day (0 would purge every read row on every tick — the
+# service clamps defensively). Default: 30.
+#OXICLOUD_NOTIFICATIONS_RETENTION_DAYS=30
+
 # Enable search functionality (default: true)
 #OXICLOUD_ENABLE_SEARCH=true