perf(call): screen-share hybrid — OS picker + WASAPI audio

Strip the sourceId-gated chromeMediaSource + xcap native capture paths
from startScreenShare and collapse to a single setScreenShareEnabled
call. Neither of the bypassed paths produced smooth frames in WebView2:
chromeMediaSource: 'desktop' is an extension-only Chromium constraint
and throws outside extension origins, and the xcap JPEG-over-IPC
fallback couldn't sustain 30fps at 1080p on a single main-thread.
setScreenShareEnabled goes through Chromium's native getDisplayMedia
capture, which is the only path that gets HW-accelerated frames into
the WebRTC encoder from WebView2.

Audio continues via the WASAPI loopback module — getDisplayMedia can't
grab system sound in WebView2 without desktop-capture entitlements
Chromium reserves for extensions. The audio track's teardown chains to
the ScreenShare video track's 'ended' event so the Windows stop-share
overlay kills both sides in lockstep.

ScreenSourcePicker is now a quality + audio chooser only; the
thumbnail grid disappears because custom source IDs don't round-trip
through WebView2, and a custom picker in front of the OS picker just
means the user picks twice.

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

apps/desktop/src-tauri/Cargo.lock

@@ -834,7 +834,7 @@ dependencies = [
 
 [[package]]
 name = "chat-app-desktop"
-version = "0.11.1"
+version = "0.11.2"
 dependencies = [
  "base64 0.22.1",
  "dryoc",