feat: server telemetry, update entity, sync-clock controls

- Server device exposing CPU/RAM/GPU/temperature/battery sensors via
  /api/v1/system/performance, plus last-restart timestamp (cached with
  jitter threshold so the recorder doesn't see poll wobble) and version.
- Update entity backed by /api/v1/system/update — installs via
  /apply, hides the install button when the server reports
  can_auto_update=false.
- Sync-clock entities: reset button, speed number, running switch, and
  the event listener now refreshes on entity_changed events too.
- Bump manifest to 0.4.0.

custom_components/ledgrab/manifest.json

@@ -8,5 +8,5 @@
   "iot_class": "local_push",
   "issue_tracker": "https://git.dolgolyov-family.by/alexei.dolgolyov/ledgrab-haos-integration/issues",
   "requirements": ["aiohttp>=3.9.0"],
-  "version": "0.2.2"
+  "version": "0.4.0"
 }