fix(ha-integration): ausgeschaltete Lampe -> "unavailable" statt Fehlerzustand

War eine Lampe stromlos, wurde der Verbindungsfehler als UpdateFailed
gemeldet; HA schob den Config-Entry in SETUP_RETRY und die Integration
fiel in den Fehlerzustand. Jetzt wird Connection-Refused/Timeout als
NinlightUnavailable gefuehrt: der Coordinator liefert den letzten
bekannten State mit available=False, der Entry bleibt geladen und die
Entity zeigt "unavailable". Protokollfehler (400, kaputtes JSON) und
Auth (401 -> Reauth) verhalten sich unveraendert.

Light-Faehigkeiten (RGB/CT, Kelvin-Bereich) sind deshalb dynamische
Properties — ein Entry, der mit stromloser Lampe angelegt wurde,
erkennt sie, sobald die Lampe antwortet.

ha-integration/custom_components/ninlight/light.py

@@ -54,17 +54,33 @@ class NinlightLight(NinlightEntity, LightEntity):
 
     def __init__(self, coordinator: NinlightCoordinator, entry: NinlightConfigEntry) -> None:
         super().__init__(coordinator, entry)
-        state = coordinator.data
         self._attr_unique_id = f"{(entry.unique_id or '').lower()}-light"
-        # Both modes are advertised for RGB bulbs: the firmware keeps the last color and
-        # the last color temperature and picks between them with `mode`, which is exactly
-        # how HA models a color_temp + rgb light.
-        self._attr_supported_color_modes = {ColorMode.COLOR_TEMP, ColorMode.RGB} if state.has_rgb else {
-            ColorMode.COLOR_TEMP
-        }
         self._attr_supported_features = LightEntityFeature.TRANSITION
-        self._attr_min_color_temp_kelvin = state.ct_min
-        self._attr_max_color_temp_kelvin = state.ct_max
+
+    # Capabilities come from the polled state, not from a one-time __init__ snapshot: an
+    # entry set up while the bulb was powered off starts from defaults and must pick up
+    # the real RGB/CT range as soon as the bulb answers again.
+    @property
+    def available(self) -> bool:
+        # An unreachable (powered-off) bulb is an expected state: the entity goes
+        # unavailable instead of the config entry erroring.
+        return self.coordinator.last_update_success and self.coordinator.data.available
+
+    @property
+    def supported_color_modes(self) -> set[ColorMode]:
+        state = self.coordinator.data
+        # Both modes for RGB bulbs: the firmware keeps the last color and the last color
+        # temperature and picks between them with `mode`, exactly how HA models a
+        # color_temp + rgb light.
+        return {ColorMode.COLOR_TEMP, ColorMode.RGB} if state.has_rgb else {ColorMode.COLOR_TEMP}
+
+    @property
+    def min_color_temp_kelvin(self) -> int:
+        return self.coordinator.data.ct_min
+
+    @property
+    def max_color_temp_kelvin(self) -> int:
+        return self.coordinator.data.ct_max
 
     @property
     def is_on(self) -> bool: