feat(call): native WASAPI system-audio for screen-share (Windows)

Hooks the custom screen-share picker up to a native WASAPI loopback
capture so "Mit System-Sound" no longer falls back to the OS picker on
Windows. Rust side opens the default render endpoint, channels 48 kHz
f32 stereo to an AudioWorklet, which feeds a MediaStreamDestination for
LiveKit to publish as ScreenShareAudio. Ring buffer sized for latency
(80 ms target, drop-to-target on overflow) and the AudioContext is
resumed eagerly so initial burstiness can't pile up.

Adds a temporary attachTrack:audio diagnostic log to confirm source
tagging matches between old and new clients.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src-tauri/Cargo.toml

@@ -57,6 +57,13 @@ windows = { version = "0.58", features = [
     "Win32_UI_WindowsAndMessaging",
 ] }
 
+# WASAPI loopback capture for system-audio screen-share. Lets the custom
+# picker hand LiveKit a real audio track without falling back to the OS
+# screen picker (which is the only way getDisplayMedia can grab system
+# sound). Windows-only for v1; macOS needs ScreenCaptureKit-audio and
+# Linux needs a PulseAudio / PipeWire path.
+wasapi = "0.15"
+
 # LiveKit client SDK — lives behind the `rust-livekit` feature flag so the
 # baseline build stays unaffected while the JS-SDK path is still the
 # default. Pulls libwebrtc-rs which adds ~20MB to the binary and ~5-10min