feat(web): add player rune store with basic actions

Core state (queue, index, state, position, duration, volume, shuffle,
repeat, error) plus actions: playQueue, togglePlay, linear skipNext,
skipPrev 3-second rule, seekTo, setVolume (localStorage-persisted),
registerAudioEl, reportTimeUpdate, reportDuration. Shuffle/repeat
logic and audio-event reporting land in follow-up commits.

Also install an in-memory Storage polyfill in vitest.setup.ts: Node 25
exposes a partial localStorage global that lacks getItem/setItem/clear
(requires --localstorage-file with a path), and jsdom defers to the
Node global when present, leaving tests unable to exercise storage.

web/vitest.setup.ts

@@ -1 +1,23 @@
 import '@testing-library/jest-dom/vitest';
+
+// Node 25 ships a partial localStorage global that lacks getItem/setItem/clear
+// unless launched with --localstorage-file. jsdom sees Node's global and skips
+// installing its own. Replace with an in-memory Storage-compatible polyfill so
+// tests (and browser-only code under test) see a working localStorage.
+class MemoryStorage implements Storage {
+  private store = new Map<string, string>();
+  get length() { return this.store.size; }
+  clear(): void { this.store.clear(); }
+  getItem(key: string): string | null { return this.store.get(key) ?? null; }
+  key(i: number): string | null { return Array.from(this.store.keys())[i] ?? null; }
+  removeItem(key: string): void { this.store.delete(key); }
+  setItem(key: string, value: string): void { this.store.set(key, String(value)); }
+}
+const memLocal = new MemoryStorage();
+const memSession = new MemoryStorage();
+Object.defineProperty(globalThis, 'localStorage', { configurable: true, value: memLocal });
+Object.defineProperty(globalThis, 'sessionStorage', { configurable: true, value: memSession });
+if (typeof window !== 'undefined') {
+  Object.defineProperty(window, 'localStorage', { configurable: true, value: memLocal });
+  Object.defineProperty(window, 'sessionStorage', { configurable: true, value: memSession });
+}