scaffold the app: tauri crate, vite front end, icons, ci

src/App.tsx

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+function App() {
+  return <div className="app" />;
+}
+
+export default App;

src/ipc.ts

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+// Placeholder. The contract lands in F3.
+import { invoke } from "@tauri-apps/api/core";
+
+export const isTauri = typeof window !== "undefined" && "__TAURI_INTERNALS__" in window;
+export const isMacDesktop =
+  isTauri && typeof navigator !== "undefined" && /mac/i.test(navigator.userAgent);
+
+export function call<T>(command: string, args?: Record<string, unknown>): Promise<T> {
+  return invoke<T>(command, args);
+}

src/main.tsx

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+import React from "react";
+import ReactDOM from "react-dom/client";
+import App from "./App";
+import { isMacDesktop } from "./ipc";
+import "./styles/tokens.css";
+import "./styles/fonts.css";
+import "./styles/app.css";
+
+// The header's lane for the traffic lights, which only one platform draws over it. Written here
+// rather than assumed by the stylesheet, so the first paint is already the right shape.
+if (isMacDesktop) document.documentElement.setAttribute("data-traffic", "");
+
+ReactDOM.createRoot(document.getElementById("root") as HTMLElement).render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>,
+);

src/styles/app.css

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+/* Placeholder. The design system replaces this in F2. */

src/styles/fonts.css

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+/* Placeholder. The design system replaces this in F2. */

src/styles/tokens.css

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+/* Placeholder. The design system replaces this in F2. */

src/vite-env.d.ts

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+/// <reference types="vite/client" />