feat(music): add Kugou (酷狗音乐) as a music source (#69)

Adds a self-contained Kugou provider (bilibili-style: direct API calls, no
embedded API server, no new npm dependency) plus full backend + WebUI wiring.

Provider (src/music/kugou.ts): search, song-url (with device registration),
lyrics (KRC decode), song detail, playlist, album, personal FM, QR login +
cookie persistence, and quality. Request signing / crypto / KRC decoding are
ported from the MIT-licensed MakcRe/KuGouMusicApi using Node's built-in
crypto and zlib (no third-party crypto packages).

Wiring: the "kugou" platform is threaded through the provider contract, queue,
play-history, bot instance/manager dispatch (getProviderFor + the -k command
flag), index/server composition, the music/player/auth routers (unified
/search/all, /quality, the platform coercions, QR login), the cookie store,
and the WebUI (search source tab + badge, SongCard badge, brand token, and a
Kugou QR/cookie login card in Settings).

Verified live during development: search, lyrics, and album playback resolve
correctly. NOT verifiable in CI (Kugou anti-bot blocks the build host's IP):
play-URL resolution, QR login, and VIP audio — these are built faithfully to
the reference and need end-to-end testing on a non-flagged IP / a Kugou
account. See the header comment in kugou.ts.

Includes src/music/kugou.test.ts (mappers + KRC→LRC). An adversarial review
pass fixed: pagination truncating on filtered counts, an ms/seconds duration
heuristic, dfid soft-fail caching, the /v5/url random-dfid fallback, the FM
body identity, and an unguarded nickname decode.

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

src/web/api/music.ts

@@ -13,7 +13,8 @@ export function createMusicRouter(
   bilibiliProvider: MusicProvider,
   logger: Logger,
   localProvider?: MusicProvider,
-  config?: BotConfig
+  config?: BotConfig,
+  kugouProvider?: MusicProvider
 ): Router {
   const router = Router();
   const youtubeProvider: MusicProvider = new YouTubeProvider();
@@ -26,6 +27,7 @@ export function createMusicRouter(
     if (platform === "bilibili") return bilibiliProvider;
     if (platform === "youtube") return youtubeProvider;
     if (platform === "local" && localProvider) return localProvider;
+    if (platform === "kugou" && kugouProvider) return kugouProvider;
     return platform === "qq" ? qqProvider : neteaseProvider;
   }
 
@@ -111,11 +113,12 @@ export function createMusicRouter(
         return;
       }
       const parsedLimit = parseInt(limit as string) || 20;
-      const [neteaseResult, qqResult, bilibiliResult, localResult] = await Promise.allSettled([
+      const [neteaseResult, qqResult, bilibiliResult, localResult, kugouResult] = await Promise.allSettled([
         neteaseProvider.search(q as string, parsedLimit),
         qqProvider.search(q as string, parsedLimit),
         bilibiliProvider.search(q as string, parsedLimit),
         localProvider && isLocalAudioEnabled() ? localProvider.search(q as string, parsedLimit) : Promise.resolve({ songs: [], albums: [], playlists: [] }),
+        kugouProvider ? kugouProvider.search(q as string, parsedLimit) : Promise.resolve({ songs: [], albums: [], playlists: [] }),
       ]);
 
       const songs = [
@@ -123,6 +126,7 @@ export function createMusicRouter(
         ...(qqResult.status === "fulfilled" ? qqResult.value.songs : []),
         ...(bilibiliResult.status === "fulfilled" ? bilibiliResult.value.songs : []),
         ...(localResult.status === "fulfilled" ? localResult.value.songs : []),
+        ...(kugouResult.status === "fulfilled" ? kugouResult.value.songs : []),
       ];
       const albums = [
         ...(neteaseResult.status === "fulfilled" ? neteaseResult.value.albums : []),
@@ -286,6 +290,7 @@ export function createMusicRouter(
       qq: qqProvider.getQuality(),
       bilibili: bilibiliProvider.getQuality(),
       local: localProvider?.getQuality() ?? "original",
+      kugou: kugouProvider?.getQuality() ?? "128",
     });
   });
 
@@ -305,6 +310,9 @@ export function createMusicRouter(
     if (!platform || platform === "bilibili") {
       bilibiliProvider.setQuality(quality);
     }
+    if ((!platform || platform === "kugou") && kugouProvider) {
+      kugouProvider.setQuality(quality);
+    }
     logger.info({ quality, platform }, "Audio quality changed");
     res.json({ success: true, quality });
   });