* feat(linux): add Quick Chat floating composer to the Tauri companion
- frameless transparent always-on-top quickchat window (on-demand, canvas
pattern), positioned top-third on the cursor monitor, CSS fade+zoom in/out
- global shortcut Ctrl+Shift+Space on X11 (GNOME reserves Alt+Space); tray
'Quick Chat' item is the Wayland entry point; blur/Esc/close-request hide
- sends via the CLI agent turn with --message-file staged 0600 (argv is
world-readable procfs) and cleaned up after the turn; failures surface as
desktop notifications; Ctrl+Enter also opens the dashboard
- default-agent identity chip (emoji/monogram) from agents list --json, 60s cache
- window-scoped capability + permission set; window-state denylist; docs
* chore(linux): register quickchat.js as a knip native-asset entry