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/switch.py

@@ -25,13 +25,19 @@ async def async_setup_entry(
     data = hass.data[DOMAIN][entry.entry_id]
     coordinator: LedGrabCoordinator = data[DATA_COORDINATOR]
 
-    entities = []
+    entities: list[SwitchEntity] = []
     if coordinator.data and "targets" in coordinator.data:
         for target_id, target_data in coordinator.data["targets"].items():
             entities.append(
                 LedGrabSwitch(coordinator, target_id, entry.entry_id)
             )
 
+    if coordinator.data:
+        for clock in coordinator.data.get("sync_clocks", []):
+            entities.append(
+                LedGrabSyncClockSwitch(coordinator, clock["id"], entry.entry_id)
+            )
+
     async_add_entities(entities)
 
 
@@ -107,3 +113,54 @@ class LedGrabSwitch(CoordinatorEntity, SwitchEntity):
         if not self.coordinator.data:
             return None
         return self.coordinator.data.get("targets", {}).get(self._target_id)
+
+
+class LedGrabSyncClockSwitch(CoordinatorEntity, SwitchEntity):
+    """Running/paused control for a sync clock.
+
+    On = clock running (linked animations advance), off = paused (frozen).
+    """
+
+    _attr_has_entity_name = True
+    _attr_icon = "mdi:clock-outline"
+
+    def __init__(
+        self,
+        coordinator: LedGrabCoordinator,
+        clock_id: str,
+        entry_id: str,
+    ) -> None:
+        super().__init__(coordinator)
+        self._clock_id = clock_id
+        self._entry_id = entry_id
+        self._attr_unique_id = f"{clock_id}_running"
+        self._attr_translation_key = "sync_clock_running"
+
+    @property
+    def device_info(self) -> dict[str, Any]:
+        return {"identifiers": {(DOMAIN, self._clock_id)}}
+
+    @property
+    def is_on(self) -> bool:
+        clock = self._get_clock()
+        if not clock:
+            return False
+        return bool(clock.get("is_running", False))
+
+    @property
+    def available(self) -> bool:
+        return self._get_clock() is not None
+
+    async def async_turn_on(self, **kwargs: Any) -> None:
+        await self.coordinator.resume_sync_clock(self._clock_id)
+
+    async def async_turn_off(self, **kwargs: Any) -> None:
+        await self.coordinator.pause_sync_clock(self._clock_id)
+
+    def _get_clock(self) -> dict[str, Any] | None:
+        if not self.coordinator.data:
+            return None
+        for clock in self.coordinator.data.get("sync_clocks", []):
+            if clock.get("id") == self._clock_id:
+                return clock
+        return None