fix(gateway): crash safety on screen-share input timeout + proper error serialization

Root cause of "langsung left": YouTube bot-block/403 on u_c1tRmj7E4 (live
stream, LOGIN_REQUIRED) made yt-dlp timeout in resolveInputWithRetry (12s).
The timeout handler did cleanup() (removing once() listeners) THEN
tee.destroy(new Error(...)) — the PassThrough emitted 'error' with NO
listener left → unhandled stream 'error' event → uncaughtException →
gracefulShutdown → bot left voice.

Fix:
- resolveInputWithRetry: tee.destroy() silently after cleanup (error carried
  in the rejection only); add permanent no-op tee.on('error') safety.
- prepareStream: output.on('error') no-op so ffmpeg spawn failure before
  playStream attaches a demux listener never crashes the gateway.
- bootstrap: serialize uncaughtException/ClientError/DB errors with
  {err, errorMsg, stack} (pino only serializes the 'err' magic key — the old
  {error: err} key printed {} so crashes were invisible).

services/discord-gateway/src/goLive/prepareStream.ts

@@ -234,6 +234,10 @@ export function prepareStream(
     }
   }
 
+  // Safety: proc may error before playStream attaches a demux listener on
+  // `output`. A no-op listener here prevents an unhandled 'error' event
+  // on the PassThrough from crashing the gateway on ffmpeg spawn failure.
+  output.on("error", () => {});
   proc.stdout?.pipe(output);
   proc.stderr?.on("data", () => {
     /* swallow ffmpeg stderr */