chore: remove unused _syncNpDirect import; add express to backend/package.json

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/package.json

@@ -2,6 +2,7 @@
   "name": "novasonic-backend",
   "private": true,
   "dependencies": {
+    "express": "^4.18.0",
     "kuromoji": "^0.1.2"
   }
 }

src/ui.js

@@ -3,7 +3,7 @@ import { esc, formatDur, toast } from './utils.js';
 import { api, coverUrl, ndAuth, fetchRomajiIndex, romajiConvert, romajiLookup, invalidateRomajiIndex, invalidateCoverCache, getRomajiOverrides, setRomajiOverride, removeRomajiOverride } from './api.js';
 import { THEMES, applyTheme, getCurrentThemeId } from './themes.js';
 // Circular imports — safe (only used inside function bodies)
-import { playQueue, dlSongLocal, toggleStar, togglePlay, renderQueue, syncNpStar, updateStarBtn, npToggleStar, playCurrent, _syncNpDirect, setPlayIcon, nativeInsertAt, refreshDisplayMode, updateNpColorMode } from './player.js';
+import { playQueue, dlSongLocal, toggleStar, togglePlay, renderQueue, syncNpStar, updateStarBtn, npToggleStar, playCurrent, setPlayIcon, nativeInsertAt, refreshDisplayMode, updateNpColorMode } from './player.js';
 import { navigate, loadPlaylists, loadPlaylistDetail } from './views.js';
 
 // ─── SIDEBAR ───