Fix RDP audio output and dynamic session resize

[allxm4]

Overview

Fixes two issues with RDP connections: no audio output and static session resolution that only CSS-scales instead of actually resizing.

• Fixed: RDP audio output not working
• Fixed: RDP session not resizing when the browser window is resized

Changes Made

Audio fix (guacamole-server.ts)
The custom connectionDefaultSettings for RDP silently wipes guacamole-lite's built-in audio: ['audio/L16'] default. Without it, guacd is told no audio formats are supported and skips the audio channel entirely. Adding audio: ["audio/L16"] back restores it.

Audio fix (GuacamoleDisplay.tsx)
client.onaudio was never handled, so incoming audio streams were silently dropped. Added a handler that passes streams to Guacamole.AudioPlayer.getInstance() for playback via the Web Audio API.

Resize fix (GuacamoleDisplay.tsx)
The existing ResizeObserver only called display.scale() — a CSS zoom that keeps the RDP session at its original resolution. Added a debounced client.sendSize(w, h) call so the RDP server is told to actually redraw at the new resolution. The backend already had "resize-method": "display-update" configured, so only the client-side signal was missing.

Type definitions (guacamole-common-js.d.ts)
Added missing sendSize, onaudio, and AudioPlayer to the type definitions.

Related Issues

None

Checklist

• Code follows project style guidelines
• Supports mobile and desktop UI/app (if applicable)
• I have read Contributing.md
• This is not a translation request