feat: RAG inline citations, source highlighting, and admin panel

- Increase RAG retrieval from 5 to 50 docs with relevance threshold (0.15)
- LLM inline citations with [来源N] format and reference list
- Clickable citation links scroll to source cards with highlight animation
- Source previews with full chunk text and answer-matched highlighting
- Message-scoped source IDs to fix cross-round citation targeting
- Admin panel pages (knowledge, users, forum, course, settings)
- Add rehype-raw dependency for HTML-in-markdown rendering

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/package.json

@@ -57,6 +57,7 @@
     "react-markdown": "^10.1.0",
     "react-syntax-highlighter": "^15.6.1",
     "rehype-katex": "^7.0.1",
+    "rehype-raw": "^7.0.0",
     "remark-gfm": "^4.0.1",
     "remark-math": "^6.0.0",
     "sonner": "^2.0.3",