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/server.ts

@@ -39,6 +39,7 @@ export interface WebServerOptions {
   qqProvider: MusicProvider;
   bilibiliProvider: MusicProvider;
   localProvider: MusicProvider;
+  kugouProvider: MusicProvider;
   database: BotDatabase;
   config: BotConfig;
   configPath: string;
@@ -124,7 +125,7 @@ export function createWebServer(options: WebServerOptions): WebServer {
   );
   app.use(
     "/api/music",
-    createMusicRouter(options.neteaseProvider, options.qqProvider, options.bilibiliProvider, logger, options.localProvider, options.config)
+    createMusicRouter(options.neteaseProvider, options.qqProvider, options.bilibiliProvider, logger, options.localProvider, options.config, options.kugouProvider)
   );
   app.use("/api/player", createPlayerRouter(
     options.botManager, logger, options.database,
@@ -132,7 +133,7 @@ export function createWebServer(options: WebServerOptions): WebServer {
   ));
   app.use(
     "/api/auth",
-    createAuthRouter(options.neteaseProvider, options.qqProvider, options.bilibiliProvider, logger, options.cookieStore)
+    createAuthRouter(options.neteaseProvider, options.qqProvider, options.bilibiliProvider, logger, options.cookieStore, options.kugouProvider)
   );
   app.use("/api/favorites", requireNotGuest, createFavoritesRouter(options.database, logger));