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/config.yml.example

@@ -80,6 +80,32 @@ general:
     device_name: "Music Mouse"
     reconnect_interval: 10.0
 
+  # Room control page ("Mein Zimmer"). Omit the whole section to hide the page. This is
+  # the opposite direction from mqtt above: it's musicmouse controlling Home Assistant
+  # entities, not the other way round. The backend proxies every call to Home
+  # Assistant's REST API with this token attached; the browser never sees it, only
+  # entity ids and display names. Home Assistant's own CORS settings do not need to
+  # allow musicmouse's origin for this - the browser only ever talks to musicmouse.
+  ha:
+    url: "http://homeassistant.local:8123"
+    # A long-lived access token, created under the HA user's own profile page.
+    token: "REPLACE_WITH_HA_LONG_LIVED_TOKEN"
+    # Cards on the room page, in this order. "name" is optional; falls back to the
+    # entity id if omitted.
+    devices:
+      - entity_id: cover.kinderzimmer_rollo
+        name: "Rollo"
+      - entity_id: light.kinderzimmer_hue_beyond_links
+        name: "Hue Beyond links"
+      - entity_id: light.kinderzimmer_deckenlampe
+        name: "Deckenlampe"
+    # Scene pill row above the cards, in this order.
+    scenes:
+      - entity_id: scene.kinderzimmer_lesen
+        name: "Lesen"
+      - entity_id: scene.kinderzimmer_gute_nacht
+        name: "Gute Nacht"
+
 # One entry per figurine. The key is the figure name and the subfolder name.
 figures:
   fuchs: