feat(kon): wire Tauri shell — thin commands, ProviderRegistry, tray

- lib.rs rewritten from scaffold to full app setup (~70 lines)
- AppState holds Arc<LocalEngine> for Whisper and Parakeet
- commands/models.rs: download, check, list, load for both engines
  Maps legacy size strings (Tiny/Base/Small/Medium) to ModelId
- commands/transcription.rs: transcribe_pcm, transcribe_file, transcribe_pcm_parakeet
  Delegates to LocalEngine.transcribe_sync() + post_process_segments()
- commands/audio.rs: save_audio via kon_audio::write_wav
- commands/windows.rs: open_task_window, open_viewer_window
- commands/llm.rs: 8 stub commands preserved for frontend compatibility
- tray.rs: extracted system tray setup (show, status, quit, click-to-show)
- Close-to-tray behaviour preserved
- All 25 v0.2 command names preserved for Svelte frontend compatibility
- clippy clean

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

src-tauri/src/tray.rs

@@ -0,0 +1,59 @@
+use tauri::image::Image;
+use tauri::menu::{MenuBuilder, MenuItemBuilder};
+use tauri::tray::TrayIconBuilder;
+use tauri::Manager;
+
+pub fn setup(app: &tauri::App) -> Result<(), Box<dyn std::error::Error>> {
+    let show = MenuItemBuilder::with_id("show", "Show Kon").build(app)?;
+    let status = MenuItemBuilder::with_id("status", "Ready")
+        .enabled(false)
+        .build(app)?;
+    let quit = MenuItemBuilder::with_id("quit", "Quit").build(app)?;
+
+    let menu = MenuBuilder::new(app)
+        .item(&show)
+        .separator()
+        .item(&status)
+        .separator()
+        .item(&quit)
+        .build()?;
+
+    let icon = app
+        .default_window_icon()
+        .cloned()
+        .unwrap_or_else(|| Image::new(&[0u8; 4], 1, 1));
+
+    let _tray = TrayIconBuilder::new()
+        .icon(icon)
+        .tooltip("Kon — Ready")
+        .menu(&menu)
+        .on_menu_event(move |app, event| match event.id().as_ref() {
+            "show" => {
+                if let Some(window) = app.get_webview_window("main") {
+                    let _ = window.show();
+                    let _ = window.set_focus();
+                }
+            }
+            "quit" => {
+                app.exit(0);
+            }
+            _ => {}
+        })
+        .on_tray_icon_event(|tray, event| {
+            if let tauri::tray::TrayIconEvent::Click {
+                button: tauri::tray::MouseButton::Left,
+                ..
+            } = event
+            {
+                if let Some(window) =
+                    tray.app_handle().get_webview_window("main")
+                {
+                    let _ = window.show();
+                    let _ = window.set_focus();
+                }
+            }
+        })
+        .build(app)?;
+
+    Ok(())
+}