feat(rdp): remote audio and a shared folder redirected as a drive

- Audio: the RDPSND channel with IronRDP's cpal playback backend (PCM;
  Opus left out to avoid another native library). On by default for new
  RDP profiles. Building now needs the ALSA headers on Linux
  (libasound2-dev), added to CI, release and fuzz jobs and the build docs.
- Shared folder (Linux/macOS): one local folder appears on the remote
  desktop as a drive. IronRDP's native backend joins server paths onto
  the share unchecked, so it is wrapped in ConfinedDrive: create, list
  and rename paths with '..' components, NUL bytes, or that resolve
  through a symlink outside the share are refused (ACCESS_DENIED);
  tests cover the escapes.

Verified against xrdp (with FUSE): the remote read the shared file, and
writes, mkdir and rename landed in the local folder. Not verified:
audio playback (the test container has no sound module), and xrdp lists
the drive as 'ignored' and can't list its directories (an IronRDP/xrdp
naming and listing mismatch, fixed upstream for the name).

docs/overview.md

@@ -148,6 +148,7 @@ Use Nexus Terminal when you need to:
 - Scale-to-fit or 1:1, a fixed resolution or one that follows the tab (Display Control).
 - Keyboard (scancodes for keys and shortcuts, Unicode for text), mouse and wheel; Ctrl+Alt+Del; text clipboard sharing in both directions.
 - Password storage modes and domain logon.
+- Remote audio playback, and a shared folder redirected as a drive (Linux and macOS), confined to that folder.
 
 ### VNC capabilities