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/components/AppHeader.tsx

@@ -1,11 +1,21 @@
 import type { ReactNode } from "react";
 
 interface Props {
+  title?: string;
+  mascot?: string;
   /** Shown next to the title when the mouse is reachable but the firmware is not. */
   status?: ReactNode;
+  /** A pill linking to the other page - there's no router, so it's a click handler
+   * rather than an `href`. */
+  link?: { label: string; onClick: () => void };
 }
 
-export function AppHeader({ status }: Props) {
+export function AppHeader({
+  title = "Musik Delphin",
+  mascot = "/dolphin-mascot.png",
+  status,
+  link,
+}: Props) {
   return (
     <div
       style={{
@@ -16,13 +26,30 @@ export function AppHeader({ status }: Props) {
         // The status bar is translucent in standalone mode, so make room for it.
         padding: "calc(18px + env(safe-area-inset-top)) 32px 6px",
         flex: "none",
+        position: "relative",
       }}
     >
-      <img
-        src="/dolphin-mascot.png"
-        alt=""
-        style={{ width: 64, height: 64, objectFit: "contain" }}
-      />
+      {link && (
+        <button
+          onClick={link.onClick}
+          style={{
+            position: "absolute",
+            left: 24,
+            border: "none",
+            cursor: "pointer",
+            background: "oklch(97% 0.01 230 / .95)",
+            color: "oklch(30% 0.03 230)",
+            fontWeight: 800,
+            fontSize: 14,
+            padding: "9px 16px",
+            borderRadius: 999,
+            boxShadow: "0 6px 18px oklch(15% 0.04 230 / .4)",
+          }}
+        >
+          {link.label}
+        </button>
+      )}
+      <img src={mascot} alt="" style={{ width: 64, height: 64, objectFit: "contain" }} />
       <div
         style={{
           fontSize: 34,
@@ -31,7 +58,7 @@ export function AppHeader({ status }: Props) {
           textShadow: "0 3px 14px oklch(15% 0.05 210 / .5)",
         }}
       >
-        Musik Delphin
+        {title}
       </div>
       {status}
     </div>