fix(guest): deny favorites + auth-status reads to guests; UI polish

Consolidated fix wave from the final whole-branch review of guest mode.

- FIX 1 (critical): gate /api/favorites mount with requireNotGuest — the
  router keys off req.user.id (shared __guest__ principal), so guests could
  read/write a shared favorites bucket. Added focused guest-deny tests.
- FIX 2: gate GET /api/auth/status and /api/auth/qrcode/status with
  requireNotGuest so config reads no longer leak to guests.
- FIX 3: requireAuthInline in createSessionRouter now rejects guest sessions
  with 401 once guest mode is disabled (mirrors createRequireAuth), so /me
  stops returning guest data after an admin disables the feature.
- FIX 4: Login guest button now sits BELOW the card (auth-page flex-direction
  column + guest-btn width 360px) instead of beside it.
- FIX 5: mobile mini-player transport buttons in App.vue are now per-button
  gated for guests (prev/play/next/mode/volume), mirroring Player.vue.
- FIX 6: refreshed stale "gated on player.control" seek comments in Player.vue
  and relabeled the now-stale quality-GET test.

npm test: 354/354 pass. npm run build: tsc + vue-tsc + vite all green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/server.ts

@@ -25,6 +25,7 @@ import { createSessionStore } from "../data/sessions.js";
 import { createPermissionStore } from "../data/permissions.js";
 import { createRequireAuth } from "./middleware/requireAuth.js";
 import { requireAdmin } from "./middleware/requireAdmin.js";
+import { requireNotGuest } from "./middleware/requireNotGuest.js";
 import { csrfOriginCheck } from "./middleware/csrf.js";
 import { createRateLimit } from "./middleware/rateLimit.js";
 import { validateSessionFromHeaders } from "./auth/validateSession.js";
@@ -126,7 +127,7 @@ export function createWebServer(options: WebServerOptions): WebServer {
     "/api/auth",
     createAuthRouter(options.neteaseProvider, options.qqProvider, options.bilibiliProvider, logger, options.cookieStore)
   );
-  app.use("/api/favorites", createFavoritesRouter(options.database, logger));
+  app.use("/api/favorites", requireNotGuest, createFavoritesRouter(options.database, logger));
 
   // admin-only routes
   app.use("/api/users", requireAdmin, createUsersRouter(users, sessions, audit, logger, permissions));