feat: add app header, sidebar, and mobile navigation components

- Implemented AppHeader component with theme toggle and connection status.
- Created AppSidebar component for navigation with connection status indicator.
- Added MobileNav component for mobile navigation with responsive design.
- Introduced shared components: DetailStat, EmptyState, ErrorState, LoadingSkeleton, and StatCard for consistent UI.
- Developed hooks for async data fetching: useAsync, useConfig, useDashboard, useGuilds, useMedia, useMessages, useRecordings, and useVoice.
- Added chatbot API functions for sending messages and managing chat history.

services/discord-gateway/src/modules/voice-recording/transmitter.ts

@@ -28,9 +28,6 @@ export class VoiceTransmitter {
   /** Set true before sending SIGTERM so exit handler knows it's intentional */
   private _expectedExit = false;
 
-  /** True while backpressure drain is in progress */
-  private draining = false;
-
   /**
    * Start listening for PCM audio data from Redis and stream to Discord
    */