feat(client-linux): log the release/disconnect keyboard chords

The Ctrl+Alt+Shift+Q/D handlers had no tracing, so a report of "the
disconnect shortcut doesn't work" was unverifiable from logs alone —
live tracing (added temporarily, then trimmed to these two lines)
showed the chord, `disconnect_quit()`, and the session teardown all
firing correctly and instantly every time; the confusion traced back
to the (now-fixed) FlowBox click crash having kept everyone from ever
reaching a live session to test the shortcut with in the first place.

Keep the two low-noise, deliberate-action log lines for the next time
this comes up; drop the per-keystroke debug trace used to diagnose it,
which would otherwise fire on every key during a stream.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

clients/linux/src/ui_stream.rs

@@ -806,6 +806,7 @@ fn attach_keyboard(
             | gdk::ModifierType::ALT_MASK
             | gdk::ModifierType::SHIFT_MASK;
         if state.contains(chord) && keyval.to_lower() == gdk::Key::q {
+            tracing::info!(captured = cap.captured.get(), "chord: Ctrl+Alt+Shift+Q (release/engage)");
             if cap.captured.get() {
                 cap.release();
             } else {
@@ -816,6 +817,7 @@ fn attach_keyboard(
         // Ctrl+Alt+Shift+D — leave the session. Now that Steam / QAM pass through to the host,
         // the capture toggle alone can't end a stream, so this is the keyboard's explicit exit.
         if state.contains(chord) && keyval.to_lower() == gdk::Key::d {
+            tracing::info!("chord: Ctrl+Alt+Shift+D (disconnect) — releasing capture + quitting");
             cap.release();
             // Deliberate user exit → close with QUIT_CLOSE_CODE so the host tears the session down
             // immediately instead of holding the keep-alive linger for a reconnect.