feat: remove old vanilla JS/CSS frontend, make React SPA the sole entry for ccw view

Remove the entire old template-based frontend (~106K lines) and make the React
SPA the only way to access the ccw dashboard via `ccw view`.

Key changes:
- Delete all old frontend files: dashboard-css/ (37 CSS), dashboard-js/ (59 JS),
  assets/, dashboard.html, and legacy HTML templates
- Delete dashboard-generator.ts and dashboard-generator-patch.ts
- Simplify server.ts: remove ~234 lines of old frontend code (template constants,
  MODULE_CSS_FILES/MODULE_FILES arrays, generateServerDashboard(), /assets/* serving)
- Rebase React frontend from /react/ to root / (vite.config.ts, react-frontend.ts)
- Add /react/* -> /* 301 redirect for backward compatibility
- Remove --frontend and --new CLI flags from view and serve commands
- Remove generateDashboard export from public API (index.ts)
- Simplify serve.ts and view.ts to always use React without conditional branching
- Update all affected tests (unit, e2e) for React-only architecture

BREAKING CHANGE: --frontend and --new CLI flags removed; generateDashboard export
removed from ccw package; /react/ base path changed to /

ccw/tests/server.test.ts

@@ -87,7 +87,11 @@ describe('server binding', async () => {
     assert.ok(sigintHandler, 'Expected serveCommand to register SIGINT handler');
 
     sigintHandler?.();
-    await new Promise((resolve) => setTimeout(resolve, 300));
+
+    // Wait for async shutdown (stopReactFrontend can take up to ~6s)
+    for (let i = 0; i < 40 && !exitCodes.includes(0); i++) {
+      await new Promise((resolve) => setTimeout(resolve, 250));
+    }
 
     rmSync(ccwHome, { recursive: true, force: true });