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/frontend/vite.config.ts

@@ -8,9 +8,9 @@ const __filename = fileURLToPath(import.meta.url)
 const __dirname = path.dirname(__filename)
 
 // Get base path from environment variable
-// Default to /react/ for development (CCW server proxies /react/* to Vite)
+// Default to / for development (CCW server proxies /* to Vite)
 // Can be overridden by VITE_BASE_URL environment variable
-const basePath = process.env.VITE_BASE_URL || '/react/'
+const basePath = process.env.VITE_BASE_URL || '/'
 
 // Backend target for Vite proxy (used when directly opening the Vite dev server port).
 // In `ccw view`, this is set to the dashboard server port so /api and /ws route correctly.