feat: add BiliBili audio source integration

Implement BiliBiliProvider for video-as-audio playback using direct
BiliBili API calls (search, video info, DASH audio URL extraction).
Add QR code login support and cookie persistence. Update FFmpeg to
send Referer header for BiliBili CDN URLs. Extend platform union type
to "netease" | "qq" | "bilibili" across all interfaces. Add -b flag
for chat commands and B站 badge in web UI.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/web/api/auth.ts

@@ -6,12 +6,14 @@ import type { Logger } from "../../logger.js";
 export function createAuthRouter(
   neteaseProvider: MusicProvider,
   qqProvider: MusicProvider,
+  bilibiliProvider: MusicProvider,
   logger: Logger,
   cookieStore?: CookieStore
 ): Router {
   const router = Router();
 
   function getProvider(platform?: string): MusicProvider {
+    if (platform === "bilibili") return bilibiliProvider;
     return platform === "qq" ? qqProvider : neteaseProvider;
   }
 
@@ -55,7 +57,8 @@ export function createAuthRouter(
       // When confirmed, persist cookie
       if (status === "confirmed") {
         const cookie = provider.getCookie();
-        const plat = (platform as string) === "qq" ? "qq" as const : "netease" as const;
+        const plat = (platform as string) === "bilibili" ? "bilibili" as const
+          : (platform as string) === "qq" ? "qq" as const : "netease" as const;
         if (cookie && cookieStore) {
           cookieStore.save(plat, cookie);
           logger.info({ platform: plat }, "Cookie persisted to disk");
@@ -118,7 +121,8 @@ export function createAuthRouter(
     }
     const provider = getProvider(platform);
     provider.setCookie(cookie);
-    const plat = platform === "qq" ? "qq" as const : "netease" as const;
+    const plat = platform === "bilibili" ? "bilibili" as const
+      : platform === "qq" ? "qq" as const : "netease" as const;
     if (cookieStore) {
       cookieStore.save(plat, cookie);
     }