feat: remove legacy frontend, root routing, compliance ZIP with Chromium PDF, chat markdown styling

- Legacy frontend removed: React SPA served at / (no /app/ prefix)
- Compliance report ZIP: Chromium headless --print-to-pdf (identical to browser) + CSV findings
- Server-side generation state: .compliance_generating marker survives page navigation
- RAG enriched: Description + Rationale + Remediation + Audit extracted from CIS vector chunks
- Chat markdown: syntax highlighting (Catppuccin), styled headings/lists/tables/blockquotes/code
- Default model auto-selected on Chat Agent load

frontend-react/src/main.tsx

@@ -6,7 +6,7 @@ import App from './App.tsx';
 
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <BrowserRouter basename="/app">
+    <BrowserRouter>
       <App />
     </BrowserRouter>
   </StrictMode>,