cameras: surface per-camera REC (record-to-disk) toggle

`enabled` already gated recording only (go2rtc/live work regardless), but
it was a buried "Вкл" checkbox. Make it an explicit REC control:
- New "Запись" column with an inline REC switch in each camera row.
- Relabel the add/edit form toggle "Вкл" -> "REC" + tooltip.
- New POST /api/cameras/{id}/record {enabled} that flips recording through
  the supervisor only (no go2rtc re-sync, so live view doesn't blip).

Off = view-only (live via go2rtc); on = record segments to disk.
VERSION -> 0.0.124.

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

backend/app/api/cameras.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 
 import asyncio
 import re
+from dataclasses import replace
 
 from fastapi import APIRouter, HTTPException, Query, Request, WebSocket, WebSocketDisconnect
 from fastapi.responses import StreamingResponse
@@ -298,3 +299,23 @@ async def clear_cameras(request: Request) -> dict:
         await runtime.supervisor.remove_camera(cam_id)
         await go2rtc.remove_camera_streams(runtime.config, cam_id)
     return {"ok": True, "removed": len(ids)}
+
+
+@router.post("/{cam_id}/record")
+async def set_record(cam_id: str, request: Request) -> dict:
+    """Включает/выключает запись камеры на диск (тумблер REC).
+
+    enabled=False — запись не идёт, но go2rtc/live не трогаем → просмотр работает.
+    Меняет только рекордер (без пересоздания go2rtc-потоков, чтобы live не мигал)."""
+    require_role(request, "admin")
+    cam = runtime.config.camera(cam_id)
+    if not cam:
+        raise HTTPException(404, "camera not found")
+    body = await request.json()
+    on = bool(body.get("enabled", True))
+    idx = next(i for i, c in enumerate(runtime.config.cameras) if c.id == cam_id)
+    new = replace(cam, enabled=on)
+    runtime.config.cameras[idx] = new
+    save_config(runtime.config)
+    await runtime.supervisor.replace_camera(new)   # старт/стоп записи; go2rtc не трогаем
+    return {"ok": True, "enabled": on}