fix(gateway): voice module critical bugs

- shutdown ordering: DB pool closed AFTER voice disconnect (was before)
- muxer: amix (mix) -> concat (sequential) filter for OGG segments
- upload retries: 0->3 with proper backoff 1-10s
- teleUpload retry backoff: minTimeout 0->1000, maxTimeout 0->10000
- mediaSource: 64KB buffer bound on readFirstTwoLines, 1MB on extractMediaInfo
- ffmpegProcess: pipe stderr to structured logger instead of inherit

Co-Authored-By: Claude <noreply@anthropic.com>

services/discord-gateway/src/app/shutdown.ts

@@ -36,19 +36,23 @@ export function createGracefulShutdown(options: GracefulShutdownOptions) {
     try {
       options.stopMetricsServer?.();
       stopMuxerWorker();
-      options.logger.info("Closing database...");
-      await options.closeDatabase();
-      options.logger.info("Database closed");
 
+      // 1. Voice disconnect (may write final DB records)
       options.logger.info("Stopping voice connection...");
       await options.voiceController.disconnect();
 
+      // 2. Close Redis/pubsub after voice is done
       options.logger.info("Closing event broadcaster...");
       await options.eventBroadcaster.close();
 
       options.logger.info("Closing command handler...");
       await options.commandHandler.close();
 
+      // 3. DB pool LAST – voice disconnect may finalize recordings
+      options.logger.info("Closing database...");
+      await options.closeDatabase();
+      options.logger.info("Database closed");
+
       options.logger.info("Destroying Discord client...");
       try {
         options.client.destroy();