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/indexer.py

@@ -80,24 +80,28 @@ class Indexer:
             await asyncio.sleep(SCAN_INTERVAL)
 
     async def scan_once(self) -> int:
-        root = self.config.storage.path
-        by_cam = _scan_segments(root)
+        active_path = self.config.active_storage().path
         known = await self.db.known_paths()
         added = 0
 
-        for cam_id, files in by_cam.items():
-            # последний файл может писаться прямо сейчас — не индексируем
-            complete = files[:-1] if len(files) > 1 else []
-            for path in complete:
-                if path in known:
-                    continue
-                duration, size = await probe_duration(path)
-                if size is None or size == 0:
-                    continue
-                await self.db.add_recording(
-                    cam_id, path, _parse_started_at(path), duration, size
-                )
-                added += 1
+        # сканируем ВСЕ хранилища: после смены активного старые записи не теряются
+        for root in self.config.storage_paths():
+            by_cam = _scan_segments(root)
+            is_active = (root == active_path)
+            for cam_id, files in by_cam.items():
+                # в активном хранилище последний файл ещё пишется — пропускаем;
+                # в неактивных все сегменты завершены, индексируем целиком.
+                complete = files[:-1] if is_active else files
+                for path in complete:
+                    if path in known:
+                        continue
+                    duration, size = await probe_duration(path)
+                    if size is None or size == 0:
+                        continue
+                    await self.db.add_recording(
+                        cam_id, path, _parse_started_at(path), duration, size
+                    )
+                    added += 1
 
         # уборка пропавших файлов
         for path in known: