feat: maintenance banner as full-screen overlay

feat: sidebar doc filter chips scope retrieval to selected documents

feat(frontend): config-driven maintenance banner in src/config.js

feat(frontend): add maintenance banner for slow upload warning

fix: remount ChatArea on workspace switch to clear stale messages

feat: multi-workspace frontend — workspace switcher, per-workspace doc list and chat

feat: add briefing UI — summary card + clickable suggested questions after upload

feat: rebrand FinRAG → Prism (collection names, system prompt, UI branding)

Add Dockerfile and Render config