Add initial project structure with essential files

- Created .gitignore to exclude build artifacts and dependencies.
- Added index.html as the main entry point for the application.
- Included LICENSE file with Apache 2.0 terms.
- Initialized package.json and package-lock.json for project dependencies.
- Added pnpm-lock.yaml for package management.
- Created QUICKSTART.md for setup instructions.
- Added README.md and README.zh-CN.md for project documentation in English and Chinese.

src/router.ts

@@ -0,0 +1,65 @@
+// Tiny URL router. We avoid pulling in react-router for two reasons:
+// the surface area we need is small (three routes, plain pushState), and
+// we want a single source of truth for "what file is open" — encoding
+// that in the URL is the simplest way to make it deep-linkable.
+
+import { useEffect, useState } from 'react';
+
+export type Route =
+  | { kind: 'home' }
+  | { kind: 'project'; projectId: string; fileName: string | null };
+
+export function parseRoute(pathname: string): Route {
+  const parts = pathname.replace(/\/+$/, '').split('/').filter(Boolean);
+  if (parts.length === 0) return { kind: 'home' };
+  if (parts[0] === 'projects' && parts[1]) {
+    const projectId = decodeURIComponent(parts[1]);
+    if (parts[2] === 'files' && parts[3]) {
+      return {
+        kind: 'project',
+        projectId,
+        fileName: decodeURIComponent(parts.slice(3).join('/')),
+      };
+    }
+    return { kind: 'project', projectId, fileName: null };
+  }
+  return { kind: 'home' };
+}
+
+export function buildPath(route: Route): string {
+  if (route.kind === 'home') return '/';
+  const id = encodeURIComponent(route.projectId);
+  if (route.fileName) {
+    const file = route.fileName
+      .split('/')
+      .map((s) => encodeURIComponent(s))
+      .join('/');
+    return `/projects/${id}/files/${file}`;
+  }
+  return `/projects/${id}`;
+}
+
+// Centralized navigation. Components call this instead of mutating
+// `window.location` directly so we can fan the change out to any
+// `useRoute()` subscriber via a custom event.
+export function navigate(route: Route, opts: { replace?: boolean } = {}): void {
+  const target = buildPath(route);
+  const current = window.location.pathname;
+  if (target === current) return;
+  if (opts.replace) {
+    window.history.replaceState(null, '', target);
+  } else {
+    window.history.pushState(null, '', target);
+  }
+  window.dispatchEvent(new PopStateEvent('popstate'));
+}
+
+export function useRoute(): Route {
+  const [route, setRoute] = useState<Route>(() => parseRoute(window.location.pathname));
+  useEffect(() => {
+    const onPop = () => setRoute(parseRoute(window.location.pathname));
+    window.addEventListener('popstate', onPop);
+    return () => window.removeEventListener('popstate', onPop);
+  }, []);
+  return route;
+}