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/api/materi.ts

@@ -1,78 +0,0 @@
-// Materi API client — talks to backend /trpc materi router
-import { createORPCClient } from "@orpc/client";
-import { RPCLink } from "@orpc/client/fetch";
-import { orpc } from "@/lib/orpc/client";
-import type { ORPCClient } from "@/lib/orpc/types";
-import type {
-  CreateMateriInput,
-  MateriDocument,
-  MateriRagChatMessage,
-  MateriRagChatResult,
-} from "@/lib/types/materi";
-
-const BACKEND_URL =
-  process.env.GMW_BACKEND_URL?.replace(/\/+$/, "") || "http://127.0.0.1:4001";
-
-let _serverClient: ORPCClient | null = null;
-function serverOrpc(): ORPCClient {
-  if (!_serverClient) {
-    const link = new RPCLink({
-      url: `${BACKEND_URL}/trpc`,
-      fetch(url, init) {
-        return fetch(url, { ...init, cache: "no-store" });
-      },
-    });
-    _serverClient = createORPCClient(link) as unknown as ORPCClient;
-  }
-  return _serverClient;
-}
-
-// Server-side (SSR seed) — uses the HTTP RPCLink via oRPC
-export async function listMateriSSR(
-  limit = 50,
-  search?: string,
-): Promise<MateriDocument[]> {
-  return (serverOrpc() as any).materi.list({
-    limit,
-    search,
-  }) as unknown as Promise<MateriDocument[]>;
-}
-
-export async function getMateriSSR(id: string): Promise<MateriDocument | null> {
-  return (serverOrpc() as any).materi.detail({
-    id,
-  }) as unknown as Promise<MateriDocument | null>;
-}
-
-// Client-side — browser WebSocket RPCLink (orpc is "use client")
-export async function createMateri(
-  input: CreateMateriInput,
-): Promise<MateriDocument> {
-  return orpc.materi.create(input) as unknown as Promise<MateriDocument>;
-}
-
-export async function updateMateri(
-  id: string,
-  input: Partial<CreateMateriInput>,
-): Promise<MateriDocument | null> {
-  return orpc.materi.update({
-    id,
-    ...input,
-  }) as unknown as Promise<MateriDocument | null>;
-}
-
-export async function deleteMateri(id: string): Promise<boolean> {
-  return orpc.materi.delete({ id }) as unknown as Promise<boolean>;
-}
-
-export async function searchMateri(
-  query: string,
-  history: MateriRagChatMessage[] = [],
-  materiId?: string,
-): Promise<MateriRagChatResult> {
-  return orpc.materi.chat({
-    message: query,
-    history,
-    materiId,
-  }) as unknown as Promise<MateriRagChatResult>;
-}