Add "Mein Zimmer" room-control page (Home Assistant, proxied through the backend)

Implements the room-control page from the design mockup: a scenes row above cards
for shutters, color lamps, and brightness-only lamps, all driven by a new
`general.ha` config section (server URL, token, ordered device/scene lists).

The backend proxies every Home Assistant call server-side (GET/POST /api/ha/...)
rather than the browser calling Home Assistant directly, so the long-lived token
never leaves the LAN device and Home Assistant's own CORS settings don't need to
know about musicmouse at all. Card kind (shutter/color/brightness-only) is
inferred at runtime from what Home Assistant reports about each entity, not
configured explicitly.

Also stops tracking python-backend/config.yml, which had drifted into the repo
despite its own header saying it shouldn't be - it now carries real credentials
locally and needs to stay untracked.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

python-backend/musicmouse/config.py

@@ -36,6 +36,8 @@ __all__ = [
     "FigureColors",
     "FigureConfig",
     "GeneralConfig",
+    "HaConfig",
+    "HaDeviceConfig",
     "LibraryConfig",
     "MqttConfig",
     "WebConfig",
@@ -173,6 +175,36 @@ class WebConfig(_Strict):
         return None if folder is None else _resolve_folder(folder, info, must_exist=False)
 
 
+class HaDeviceConfig(_Strict):
+    """One Home Assistant entity to expose to the room-control page ("Mein Zimmer")."""
+
+    entity_id: str
+    name: str | None = None
+
+
+class HaConfig(_Strict):
+    """Home Assistant integration for the room-control page ("Mein Zimmer").
+
+    The backend never calls Home Assistant itself - it only hands the browser the
+    server URL, the token, and these two ordered lists. Control happens directly from
+    the browser to Home Assistant's own REST API, so this token grants full HA control
+    to anything on the LAN that can reach musicmouse. See config.yml.example.
+    """
+
+    url: str
+    token: str
+    #: Order is preserved and drives the device card grid on the room page.
+    devices: list[HaDeviceConfig] = Field(default_factory=list)
+    #: Order is preserved and drives the scene pill row on the room page.
+    scenes: list[HaDeviceConfig] = Field(default_factory=list)
+
+    @model_validator(mode="after")
+    def _check_something_configured(self) -> Self:
+        if not self.devices and not self.scenes:
+            raise ValueError("configure at least one device or scene, or omit the ha section")
+        return self
+
+
 class GeneralConfig(_Strict):
     library: LibraryConfig
 
@@ -188,6 +220,7 @@ class GeneralConfig(_Strict):
 
     mqtt: MqttConfig | None = None
     web: WebConfig | None = None
+    ha: HaConfig | None = None
 
     min_volume: int = Field(default=0, ge=0, le=200)
     max_volume: int = Field(default=100, ge=0, le=200)