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>

web/src/main.tsx

@@ -3,6 +3,7 @@ import { createRoot } from "react-dom/client";
 
 import { App } from "./App";
 import "./styles/app.css";
+import "./styles/room.css";
 
 createRoot(document.getElementById("root")!).render(
   <StrictMode>