chore: hapus fitur materi (learning materials + RAG chat)

Hapus fitur materi seluruhnya dari GMW monorepo:

Backend:
- Hapus module materi/ (index.ts, materi.repository.ts, materi.schema.ts,
  materi.service.ts, ragClient.ts)
- Hapus materiRouter dari orpc/router.ts (imports, const, appRouter entry)
- Hapus pgMateriDocumentsTable + types dari shared/database/schema.ts

Frontend:
- Hapus route pages app/(dashboard)/materi/ (page, [id], chat, new)
- Hapus lib/api/materi.ts (oRPC client wrappers)
- Hapus lib/types/materi.ts + export dari index.ts
- Hapus nav item "Materi" dari lib/navigation.ts + unused BookOpen import

Scripts:
- Hapus scripts/add-materi-documents.sql
- Tambah scripts/drop-materi-documents.sql (ops DB cleanup)

Verification:
- Backend: npx tsc --noEmit — clean (exit 0)
- Frontend: npx tsc --noEmit — clean (exit 0)
- Grep: zero materi code references remaining (hanya di drop-materi-documents.sql)

RAG dependencies (messages/embed.ts, messages/qdrant.ts) tetap karena juga
dipakai oleh messages.service.ts.

services/frontend/src/lib/navigation.ts

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