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/styles/room.css

@@ -0,0 +1,54 @@
+/* "Mein Zimmer" (room control). Ported from claude-design/Mein Zimmer.dc.html - the
+   same oklch-everywhere approach as app.css, but its own violet hue (~298-310) rather
+   than app.css's teal (~210), so the two pages read as siblings, not one bleeding into
+   the other. */
+
+:root {
+  --room-ink: oklch(20% 0.03 300);
+  --room-paper: oklch(97% 0.01 302);
+  --room-accent: oklch(62% 0.15 302);
+  --room-card-bg: oklch(96% 0.012 300 / 0.55);
+  --room-shadow: oklch(15% 0.05 300 / 0.35);
+}
+
+.room-stage {
+  background: linear-gradient(
+    180deg,
+    oklch(56% 0.14 305) 0%,
+    oklch(38% 0.12 300) 45%,
+    oklch(21% 0.08 298) 100%
+  );
+}
+
+.room-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
+  gap: 20px;
+}
+
+.room-card {
+  background: var(--room-card-bg);
+  backdrop-filter: blur(6px);
+  border-radius: 22px;
+  padding: 18px 20px 20px;
+  box-shadow: 0 8px 24px var(--room-shadow);
+}
+
+.room-pill {
+  border: none;
+  cursor: pointer;
+  font-size: 15px;
+  font-weight: 800;
+  min-height: 52px;
+  padding: 12px 20px;
+  border-radius: 999px;
+  white-space: nowrap;
+  background: oklch(97% 0.01 302 / 0.18);
+  color: var(--room-paper);
+}
+
+.room-pill[data-active="true"] {
+  background: var(--room-paper);
+  color: oklch(26% 0.05 300);
+  box-shadow: 0 6px 18px oklch(15% 0.05 300 / 0.4);
+}