feat: Tauri desktop GUI app with call engine

- New desktop/ directory with Tauri v2 + Vite + TypeScript
- Rust backend: CallEngine wrapping wzp-client audio + transport
- Web frontend: connect screen, in-call screen with participants,
  mic/speaker mute, keyboard shortcuts (m/s/q)
- Dark theme UI, settings persistence via localStorage
- Platform-aware --os-aec: warns on Windows/Linux (not yet implemented)
- Workspace updated to include desktop/src-tauri

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

desktop/src-tauri/src/main.rs

@@ -0,0 +1,155 @@
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+mod engine;
+
+use engine::CallEngine;
+use serde::Serialize;
+use std::sync::Arc;
+use tauri::Emitter;
+use tokio::sync::Mutex;
+
+#[derive(Clone, Serialize)]
+struct CallEvent {
+    kind: String,
+    message: String,
+}
+
+#[derive(Clone, Serialize)]
+struct Participant {
+    fingerprint: String,
+    alias: Option<String>,
+}
+
+#[derive(Clone, Serialize)]
+struct CallStatus {
+    active: bool,
+    mic_muted: bool,
+    spk_muted: bool,
+    participants: Vec<Participant>,
+    encode_fps: u64,
+    recv_fps: u64,
+}
+
+struct AppState {
+    engine: Mutex<Option<CallEngine>>,
+}
+
+#[tauri::command]
+async fn connect(
+    state: tauri::State<'_, Arc<AppState>>,
+    app: tauri::AppHandle,
+    relay: String,
+    room: String,
+    alias: String,
+    os_aec: bool,
+) -> Result<String, String> {
+    let mut engine_lock = state.engine.lock().await;
+    if engine_lock.is_some() {
+        return Err("already connected".into());
+    }
+
+    let app_clone = app.clone();
+    match CallEngine::start(relay, room, alias, os_aec, move |event_kind, message| {
+        let _ = app_clone.emit(
+            "call-event",
+            CallEvent {
+                kind: event_kind.to_string(),
+                message: message.to_string(),
+            },
+        );
+    })
+    .await
+    {
+        Ok(eng) => {
+            *engine_lock = Some(eng);
+            Ok("connected".into())
+        }
+        Err(e) => Err(format!("{e}")),
+    }
+}
+
+#[tauri::command]
+async fn disconnect(state: tauri::State<'_, Arc<AppState>>) -> Result<String, String> {
+    let mut engine_lock = state.engine.lock().await;
+    if let Some(engine) = engine_lock.take() {
+        engine.stop().await;
+        Ok("disconnected".into())
+    } else {
+        Err("not connected".into())
+    }
+}
+
+#[tauri::command]
+async fn toggle_mic(state: tauri::State<'_, Arc<AppState>>) -> Result<bool, String> {
+    let engine_lock = state.engine.lock().await;
+    if let Some(ref engine) = *engine_lock {
+        let muted = engine.toggle_mic();
+        Ok(muted)
+    } else {
+        Err("not connected".into())
+    }
+}
+
+#[tauri::command]
+async fn toggle_speaker(state: tauri::State<'_, Arc<AppState>>) -> Result<bool, String> {
+    let engine_lock = state.engine.lock().await;
+    if let Some(ref engine) = *engine_lock {
+        let muted = engine.toggle_speaker();
+        Ok(muted)
+    } else {
+        Err("not connected".into())
+    }
+}
+
+#[tauri::command]
+async fn get_status(state: tauri::State<'_, Arc<AppState>>) -> Result<CallStatus, String> {
+    let engine_lock = state.engine.lock().await;
+    if let Some(ref engine) = *engine_lock {
+        let status = engine.status();
+        Ok(CallStatus {
+            active: true,
+            mic_muted: status.mic_muted,
+            spk_muted: status.spk_muted,
+            participants: status
+                .participants
+                .into_iter()
+                .map(|p| Participant {
+                    fingerprint: p.fingerprint,
+                    alias: p.alias,
+                })
+                .collect(),
+            encode_fps: status.frames_sent,
+            recv_fps: status.frames_received,
+        })
+    } else {
+        Ok(CallStatus {
+            active: false,
+            mic_muted: false,
+            spk_muted: false,
+            participants: vec![],
+            encode_fps: 0,
+            recv_fps: 0,
+        })
+    }
+}
+
+fn main() {
+    tracing_subscriber::fmt().init();
+
+    let state = Arc::new(AppState {
+        engine: Mutex::new(None),
+    });
+
+    tauri::Builder::default()
+        .plugin(tauri_plugin_shell::init())
+        .manage(state)
+        .invoke_handler(tauri::generate_handler![
+            connect,
+            disconnect,
+            toggle_mic,
+            toggle_speaker,
+            get_status,
+        ])
+        .run(tauri::generate_context!())
+        .expect("error while running WarzonePhone Desktop");
+}