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/main.ts

@@ -0,0 +1,177 @@
+import { invoke } from "@tauri-apps/api/core";
+import { listen } from "@tauri-apps/api/event";
+
+// Elements
+const connectScreen = document.getElementById("connect-screen")!;
+const callScreen = document.getElementById("call-screen")!;
+const relayInput = document.getElementById("relay") as HTMLInputElement;
+const roomInput = document.getElementById("room") as HTMLInputElement;
+const aliasInput = document.getElementById("alias") as HTMLInputElement;
+const osAecCheckbox = document.getElementById("os-aec") as HTMLInputElement;
+const connectBtn = document.getElementById("connect-btn") as HTMLButtonElement;
+const connectError = document.getElementById("connect-error")!;
+const roomName = document.getElementById("room-name")!;
+const participantsDiv = document.getElementById("participants")!;
+const micBtn = document.getElementById("mic-btn")!;
+const spkBtn = document.getElementById("spk-btn")!;
+const hangupBtn = document.getElementById("hangup-btn")!;
+const statsDiv = document.getElementById("stats")!;
+
+let statusInterval: number | null = null;
+
+// Load saved settings
+const saved = localStorage.getItem("wzp-settings");
+if (saved) {
+  try {
+    const s = JSON.parse(saved);
+    if (s.relay) relayInput.value = s.relay;
+    if (s.room) roomInput.value = s.room;
+    if (s.alias) aliasInput.value = s.alias;
+    if (s.osAec !== undefined) osAecCheckbox.checked = s.osAec;
+  } catch {}
+}
+
+function saveSettings() {
+  localStorage.setItem(
+    "wzp-settings",
+    JSON.stringify({
+      relay: relayInput.value,
+      room: roomInput.value,
+      alias: aliasInput.value,
+      osAec: osAecCheckbox.checked,
+    })
+  );
+}
+
+// Connect
+connectBtn.addEventListener("click", async () => {
+  connectError.textContent = "";
+  connectBtn.disabled = true;
+  connectBtn.textContent = "Connecting...";
+  saveSettings();
+
+  try {
+    await invoke("connect", {
+      relay: relayInput.value,
+      room: roomInput.value,
+      alias: aliasInput.value,
+      osAec: osAecCheckbox.checked,
+    });
+    showCallScreen();
+  } catch (e: any) {
+    connectError.textContent = String(e);
+    connectBtn.disabled = false;
+    connectBtn.textContent = "Connect";
+  }
+});
+
+function showCallScreen() {
+  connectScreen.classList.add("hidden");
+  callScreen.classList.remove("hidden");
+  roomName.textContent = roomInput.value;
+
+  // Poll status
+  statusInterval = window.setInterval(pollStatus, 500);
+}
+
+function showConnectScreen() {
+  callScreen.classList.add("hidden");
+  connectScreen.classList.remove("hidden");
+  connectBtn.disabled = false;
+  connectBtn.textContent = "Connect";
+  if (statusInterval) {
+    clearInterval(statusInterval);
+    statusInterval = null;
+  }
+}
+
+// Mute buttons
+micBtn.addEventListener("click", async () => {
+  try {
+    const muted: boolean = await invoke("toggle_mic");
+    micBtn.classList.toggle("muted", muted);
+  } catch {}
+});
+
+spkBtn.addEventListener("click", async () => {
+  try {
+    const muted: boolean = await invoke("toggle_speaker");
+    spkBtn.classList.toggle("muted", muted);
+  } catch {}
+});
+
+// Hangup
+hangupBtn.addEventListener("click", async () => {
+  try {
+    await invoke("disconnect");
+  } catch {}
+  showConnectScreen();
+});
+
+// Keyboard shortcuts
+document.addEventListener("keydown", (e) => {
+  if (callScreen.classList.contains("hidden")) return;
+  if (e.key === "m") micBtn.click();
+  if (e.key === "s") spkBtn.click();
+  if (e.key === "q") hangupBtn.click();
+});
+
+// Status polling
+interface CallStatus {
+  active: boolean;
+  mic_muted: boolean;
+  spk_muted: boolean;
+  participants: { fingerprint: string; alias: string | null }[];
+  encode_fps: number;
+  recv_fps: number;
+}
+
+async function pollStatus() {
+  try {
+    const status: CallStatus = await invoke("get_status");
+    if (!status.active) {
+      showConnectScreen();
+      return;
+    }
+
+    // Update mute state
+    micBtn.classList.toggle("muted", status.mic_muted);
+    spkBtn.classList.toggle("muted", status.spk_muted);
+
+    // Update participants
+    participantsDiv.innerHTML = status.participants
+      .map((p) => {
+        const name = p.alias || "Anonymous";
+        const initial = name.charAt(0).toUpperCase();
+        const fp = p.fingerprint
+          ? p.fingerprint.substring(0, 8) + "..."
+          : "";
+        return `
+          <div class="participant">
+            <div class="avatar">${initial}</div>
+            <div class="info">
+              <div class="name">${escapeHtml(name)}</div>
+              <div class="fp">${escapeHtml(fp)}</div>
+            </div>
+          </div>`;
+      })
+      .join("");
+
+    // Stats
+    statsDiv.textContent = `TX: ${status.encode_fps} frames | RX: ${status.recv_fps} frames`;
+  } catch {}
+}
+
+function escapeHtml(s: string): string {
+  const d = document.createElement("div");
+  d.textContent = s;
+  return d.innerHTML;
+}
+
+// Listen for events from backend
+listen("call-event", (event: any) => {
+  const { kind, message } = event.payload;
+  if (kind === "room-update") {
+    pollStatus();
+  }
+});