Merge the typing game into the music player as a tab, with lock/unlock UI

Moves tippen from a standalone app into web/ as a third tab (audio player /
smarthome / typing), replacing the old single room-toggle corner button with a
vertical icon tab rail. Curriculum and progress now come from the backend
(musicmouse/tippen/*) instead of a build-time YAML import and localStorage.

Adds reward-driven lock rendering: Cover/BrowseView/AlbumModal show a question
mark for locked albums/tracks with a hint on what unlocks them, and
ResultSheet gets a new unlock-animation block alongside the existing
lesson-unlock and aquarium-creature celebrations.

CSS from the two apps is merged carefully: identical rules (bubble/card/
key-cap/view-enter/backdrop-enter and their keyframes) are shared as-is,
while rules that bake in each app's own hue are kept separate under a
`tp-` prefix and scoped to the typing tab's own .tp-stage wrapper, so
neither app's look bleeds into the other's.

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

web/src/main.tsx

@@ -4,6 +4,7 @@ import { createRoot } from "react-dom/client";
 import { App } from "./App";
 import "./styles/app.css";
 import "./styles/room.css";
+import "./styles/tippen.css";
 
 createRoot(document.getElementById("root")!).render(
   <StrictMode>