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/api/materi.ts

@@ -0,0 +1,65 @@
+// 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 { MateriDocument, CreateMateriInput, MateriRagChatResult, MateriRagChatMessage } from "@/lib/types/materi";
+import type { ORPCClient } from "@/lib/orpc/types";
+
+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>;
+}