Fix corner cases in connect/disconnect lifecycle and resource cleanup

1. Move TS6 handler patch to after client.connect() — the library's
   connect() internally replaces handler via #S(), discarding any
   patch applied beforehand. Patching after connect() is safe because
   clientinit is sent in async message callbacks after Init1 round-trips.

2. Preserve detectedProtocol across reconnect — disconnect() resets it
   to "unknown", causing the TS6 patch to be skipped on reconnect.

3. Prevent double "disconnected" event in BotInstance — disconnect()
   emitted it directly AND the async TS3Client disconnect triggered
   another through the event chain.

4. Guard playNext() against running after disconnect — check connected
   flag to avoid ghost queue processing.

5. Fix UDP error timer leak — clear previous timer before setting a new
   one to prevent accumulation.

6. Fix isPortFree() FD leak — close the test server on error path.

https://claude.ai/code/session_01QzvMLUT3UkhsffShcY1qzD

src/music/api-server.ts

@@ -17,7 +17,9 @@ export interface ApiServerManager {
 function isPortFree(port: number): Promise<boolean> {
   return new Promise((resolve) => {
     const server = net.createServer();
-    server.once("error", () => resolve(false));
+    server.once("error", () => {
+      server.close(() => resolve(false));
+    });
     server.once("listening", () => {
       server.close(() => resolve(true));
     });