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)

services/frontend/src/lib/navigation.ts

@@ -1,4 +1,5 @@
 import {
+  BookOpen,
   Headphones,
   LayoutDashboard,
   type LucideIcon,
@@ -63,6 +64,12 @@ export const navItems: NavItem[] = [
     icon: Search,
     matchPrefix: "/analysis",
   },
+  {
+    href: "/materi",
+    label: "Materi",
+    icon: BookOpen,
+    matchPrefix: "/materi",
+  },
 ];
 
 /**