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/settings.rs

@@ -1,2 +1,34 @@
-// Settings commands — app preferences, model selection, AI provider config
-// TODO: Implement when settings UI is built
+use serde_json::{json, Value};
+use std::fs;
+use std::path::PathBuf;
+
+use crate::llama::LlamaManager;
+
+fn settings_path() -> PathBuf {
+    LlamaManager::data_dir().join("settings.json")
+}
+
+/// Load app settings from disk.
+#[tauri::command]
+pub fn load_settings() -> Value {
+    let path = settings_path();
+    if !path.exists() {
+        return json!({});
+    }
+    match fs::read_to_string(&path) {
+        Ok(content) => serde_json::from_str(&content).unwrap_or(json!({})),
+        Err(_) => json!({}),
+    }
+}
+
+/// Save app settings to disk.
+#[tauri::command]
+pub fn save_settings(settings: Value) -> Result<(), String> {
+    let path = settings_path();
+    if let Some(parent) = path.parent() {
+        fs::create_dir_all(parent).map_err(|e| format!("Cannot create settings dir: {e}"))?;
+    }
+    let json = serde_json::to_string_pretty(&settings).map_err(|e| e.to_string())?;
+    fs::write(&path, json).map_err(|e| format!("Cannot write settings: {e}"))?;
+    Ok(())
+}