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>

backend/app/recorder/supervisor.py

@@ -21,10 +21,15 @@ class Supervisor:
         # запись основного потока идёт через рестрим go2rtc (одна сессия к камере)
         return go2rtc.restream_main_url(self.config, cam.id)
 
+    def _new_task(self, cam: Camera) -> RecorderTask:
+        # пишем в активное хранилище; смена активного → restart_all репойнтит все задачи
+        active = self.config.active_storage()
+        return RecorderTask(cam, active, self.config.storage.segment_seconds,
+                            on_status=self.on_status, input_url=self._input_url(cam))
+
     def start_all(self) -> None:
         for cam in self.config.cameras:
-            task = RecorderTask(cam, self.config.storage, on_status=self.on_status,
-                                input_url=self._input_url(cam))
+            task = self._new_task(cam)
             self.tasks[cam.id] = task
             if cam.enabled and cam.record:
                 task.start()
@@ -57,8 +62,7 @@ class Supervisor:
 
     def add_camera(self, cam: Camera) -> None:
         """Создаёт задачу записи для новой камеры и запускает (если включена)."""
-        task = RecorderTask(cam, self.config.storage, on_status=self.on_status,
-                            input_url=self._input_url(cam))
+        task = self._new_task(cam)
         self.tasks[cam.id] = task
         if cam.enabled and cam.record:
             task.start()