storage: multi-storage management with per-storage quota

Replace the single fixed /records path with a list of storages and an
active selection (where new recordings go). Quota is now per-storage.

- config: StorageItem(id,name,type,path,quota_gb,nas-meta) + Storage keeps
  global retention_days/segment_seconds; active + items. Migration from the
  old single {path,quota_gb} schema → one local item.
- recorder: write to the active storage; restart_all() repoints on switch;
  NAS-not-mounted guard (never write into the container overlay).
- indexer: scan ALL storage roots so recordings survive an active switch.
- retention: enforce quota PER storage via db.total_size_under /
  oldest_recordings_under (path-prefix LIKE).
- api/storages: GET/POST/PUT/DELETE + activate + policy. NAS uses host-mount
  (backend stores SMB params, generates the mount/fstab command, reports
  ismount status). Retire old POST /api/storage.
- frontend: new "Хранилища" settings tab — table with inline per-row quota,
  add form (local folder / NAS SMB), global policy (segment + retention).
- compose: add shared ./storages:/storages root for extra local folders and
  host-mounted NAS shares.

VERSION 0.0.127.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -20,10 +20,13 @@ services:
       - ./backend/app:/app/app    # код бэкенда (правка без пересборки образа)
       - ./frontend:/app/frontend  # фронтенд (правка без пересборки)
       - ./data:/data              # SQLite-индекс архива
-      # Запись. Локальная папка ./records ИЛИ смонтированный на хост NAS (SMB/NFS).
-      # Для NAS: смонтируйте на хосте (например /mnt/nas/cctv) и замените левую часть:
-      #   - /mnt/nas/cctv:/records
+      # Запись. ./records — дефолтное локальное хранилище (id=local).
       - ./records:/records
+      # Общий корень доп. хранилищ (вкладка «Хранилища»): локальные подпапки
+      # /storages/<id> и точки монтирования NAS. NAS монтируется на ХОСТЕ в
+      # ./storages/<id>; после `mount` на хосте выполните `docker compose up -d`,
+      # чтобы том стал виден здесь (или добавьте :rshared для live-подхвата).
+      - ./storages:/storages
     environment:
       TZ: Europe/Moscow
       NVR_CONFIG: /app/cameras.yaml