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/commands/llm.rs

@@ -0,0 +1,53 @@
+// LLM stubs — ONNX-based local LLM coming post-revenue.
+
+#[tauri::command]
+pub fn check_llm_engine() -> Result<bool, String> {
+    Ok(false)
+}
+
+#[tauri::command]
+pub fn check_llm_model(_size: String) -> Result<bool, String> {
+    Ok(false)
+}
+
+#[tauri::command]
+pub fn list_llm_models() -> Result<Vec<String>, String> {
+    Ok(vec![])
+}
+
+#[tauri::command]
+pub async fn download_llm_model(
+    _app: tauri::AppHandle,
+    _size: String,
+) -> Result<String, String> {
+    Err("LLM not available yet — coming soon".into())
+}
+
+#[tauri::command]
+pub async fn load_llm_model(
+    _size: String,
+) -> Result<String, String> {
+    Err("LLM not available yet — coming soon".into())
+}
+
+#[tauri::command]
+pub async fn llm_generate(
+    _prompt: String,
+    _max_tokens: Option<u32>,
+) -> Result<String, String> {
+    Err("LLM not available yet — coming soon".into())
+}
+
+#[tauri::command]
+pub async fn llm_extract_tasks(
+    _transcript: String,
+) -> Result<Vec<String>, String> {
+    Err("LLM not available yet — coming soon".into())
+}
+
+#[tauri::command]
+pub async fn llm_format_transcript(
+    _transcript: String,
+) -> Result<String, String> {
+    Err("LLM not available yet — coming soon".into())
+}