feat: add Materi section + AI agent RAG to GMW business flow
Backend:
- New materi module: schema (materi_documents table), repository, service
- ragClient: semantic + keyword search over materi docs, plus Discord
archive via Qdrant, then LLM answer generation (RAG)
- Wire materiRouter into appRouter (list/detail/create/update/delete/chat)
Frontend:
- New types (MateriDocument, CreateMateriInput, RAG chat shapes)
- API client (SSR HTTP RPCLink + browser WS RPCLink)
- Routes: /materi list, /materi/[id] detail, /materi/new form,
/materi/chat RAG chat UI
- Sidebar nav item 'Materi'
Migration: scripts/add-materi-documents.sql (CREATE TABLE IF NOT EXISTS)