agent: wayland — evdev hotkey backend, download resume, SHA256 integrity

Add kon-hotkey crate with evdev-based global hotkey capture that works on
Wayland (and X11). Patterns from whisper-overlay: per-device async listeners,
inotify hotplug with udev permission retry, watch channel for live config
updates. Frontend detects Wayland at startup and selects evdev or
tauri-plugin-global-shortcut automatically.

Model downloads now support HTTP Range resume for interrupted downloads and
optional SHA256 integrity verification (incremental, no second pass).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -107,6 +107,8 @@ pub fn run() {
             // Store init script for secondary windows (float, viewer)
             app.manage(PreferencesScript(init_script));
 
+            app.manage(commands::hotkey::HotkeyState::new());
+
             app.manage(AppState {
                 whisper_engine: Arc::new(LocalEngine::new(
                     EngineName::new("whisper"),
@@ -152,6 +154,12 @@ pub fn run() {
             // Hardware
             commands::hardware::probe_system,
             commands::hardware::rank_models,
+            // Hotkey (evdev — Wayland-compatible)
+            commands::hotkey::is_wayland_session,
+            commands::hotkey::check_hotkey_access,
+            commands::hotkey::start_evdev_hotkey,
+            commands::hotkey::update_evdev_hotkey,
+            commands::hotkey::stop_evdev_hotkey,
         ])
         .run(tauri::generate_context!())
         .expect("error while running Kon");