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

docker-compose.yml

@@ -25,9 +25,9 @@ services:
     container_name: oci-agent-frontend
     restart: unless-stopped
     volumes:
-      - ./frontend/index.html:/usr/share/nginx/html/index.html:ro
       - ./frontend-react/dist:/usr/share/nginx/html/app:ro
       - ./nginx/default.conf:/etc/nginx/conf.d/default.conf:ro
+    # Note: nginx root points to /usr/share/nginx/html/app (React dist)
     ports:
       - "${PORT:-8080}:80"
     depends_on: