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/audio/player.ts

@@ -58,11 +58,21 @@ export class AudioPlayer extends EventEmitter {
 
     this.logger.info({ url: url.slice(0, 80), seek: seekSeconds }, "Starting playback");
 
-    const args = [
+    const args: string[] = [];
+
+    // BiliBili CDN requires Referer header for audio playback
+    if (url.includes("bilivideo") || url.includes("bilibili")) {
+      args.push(
+        "-headers",
+        "Referer: https://www.bilibili.com\r\nUser-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36\r\n"
+      );
+    }
+
+    args.push(
       "-reconnect", "1",
       "-reconnect_streamed", "1",
       "-reconnect_delay_max", "5",
-    ];
+    );
     if (seekSeconds > 0) {
       args.push("-ss", String(seekSeconds));
     }

src/audio/queue.ts

@@ -10,7 +10,7 @@ export interface QueuedSong {
   name: string;
   artist: string;
   album: string;
-  platform: "netease" | "qq";
+  platform: "netease" | "qq" | "bilibili";
   url?: string; // resolved lazily at play time
   coverUrl: string;
   duration: number; // seconds