Phase 6: Llama-server manager, settings UI, packaging, and polish

- Implement LlamaManager in Rust for llama-server lifecycle: spawn with
  port allocation, health check, clean shutdown on Drop, model listing
- Add llama_start/stop/status/list_models Tauri commands
- Add load_settings/save_settings commands with JSON persistence
- Build SettingsModal with tabs for Transcription, AI Provider, Local AI
  settings (model size, device, language, API keys, provider selection)
- Wire settings into pipeline calls (model, device, language, skip diarization)
- Configure Tauri packaging: asset protocol for local audio files,
  CSP policy, bundle metadata, Linux .deb/.AppImage and Windows .msi config
- Add keyboard shortcuts: Space (play/pause), Ctrl+O (import),
  Ctrl+, (settings), Escape (close menus/modals)
- Close export dropdown on outside click
- Tests: 30 Python, 6 Rust, 0 Svelte errors

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/commands/ai.rs

@@ -25,7 +25,7 @@ pub fn ai_chat(
     let manager = get_sidecar()?;
 
     let request_id = uuid::Uuid::new_v4().to_string();
-    let mut payload = json!({
+    let payload = json!({
         "action": "chat",
         "messages": messages,
         "transcript_context": transcript_context.unwrap_or_default(),