Message actions + citation Sources (#97, #98) (#101)

## Summary
- Closes [#97](#97) — message action row: copy (raw markdown + code-block copy), thumbs up/down with optimistic updates + down-reason popover, and export menu (PDF / DOCX / CSV / XLSX / TXT) for a single message plus conversation-level export in the chat toolbar.
- Closes [#98](#98) — versioned WS `citations` frame parsing, Sources list under assistant bubbles, clickable `[n]` markers, and history hydrate from `Prompt.citations`.
- Backend companion for ratings: [chat_backend#67](ai_ml_operations/chat_backend#67). Thumbs UI posts to `prompt_feedback` once that lands; votes rehydrate from `conversation_details.feedback`.
- Export libs (`pdfmake`, `docx`, `papaparse`, `xlsx`) are dynamically imported so they stay out of the main path until used.

## Test plan
- [ ] Stream a grounded answer → Sources appear after stream; inline `[n]` highlights the matching source; reload keeps Sources.
- [ ] Non-grounded turn → no Sources header.
- [ ] Copy message + code block; confirm checkmark ~2s; failure path shows toast.
- [ ] Thumbs up/down optimistic UI; clear by re-click; down opens reason popover without blocking the vote (needs chat_backend#67).
- [ ] Export one message and whole conversation in all five formats; check searchable PDF text and DOCX structure.
- [ ] Action row: hover reveal on desktop, always visible on last/touch; hidden while streaming.
- [ ] `npm test -- --testPathPattern='wsFrames|clipboard|exportChat|promptFeedback|ConversationDetailCard'`Reviewed-on: #101

llm-fe/package.json

@@ -21,16 +21,21 @@
     "@testing-library/user-event": "^14.5.2",
     "@types/jest": "^29.5.14",
     "@types/node": "^22.10.2",
+    "@types/papaparse": "^5.5.2",
+    "@types/pdfmake": "^0.3.3",
     "axios": "^1.13.2",
     "babel-loader": "^9.2.1",
     "bootstrap": "^5.3.3",
     "brace-expansion": "file:vendor/brace-expansion-compat",
     "chroma-js": "^3.1.2",
+    "docx": "^9.7.1",
     "formik": "^2.4.6",
     "jwt-decode": "^4.0.0",
     "lodash": "^4.17.21",
     "markdown-to-jsx": "^7.7.2",
     "mini.css": "^3.0.1",
+    "papaparse": "^5.5.4",
+    "pdfmake": "^0.3.11",
     "react-bootstrap": "^2.10.6",
     "react-code-blocks": "^0.1.6",
     "react-github-btn": "^1.4.0",
@@ -43,6 +48,7 @@
     "web-vitals": "^4.2.4",
     "webpack": "^5.97.1",
     "webpack-cli": "^5.1.4",
+    "xlsx": "^0.18.5",
     "yup": "^1.5.0"
   },
   "scripts": {
@@ -80,6 +86,7 @@
   },
   "devDependencies": {
     "@capacitor/assets": "^3.0.5",
+    "@testing-library/dom": "^10.4.1",
     "@types/bootstrap": "~5.2.10",
     "@types/lodash": "~4.17.13",
     "@types/react": "^18.3.16",