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/backend/src/modules/materi/materi.repository.ts

@@ -0,0 +1,148 @@
+import { and, desc, eq, ilike, or, sql } from "drizzle-orm";
+import {
+  type MateriDocument,
+  materiDocumentsTable,
+} from "@/shared/database/schema.js";
+import { getDatabase } from "@/shared/database/index.js";
+import type { MateriQueryInput } from "./materi.schema.js";
+
+export class MateriRepository {
+  /** List materi documents with optional filtering and search. */
+  async list(input: MateriQueryInput): Promise<MateriDocument[]> {
+    const db = getDatabase();
+
+    const conditions = [];
+
+    // Text search across title and content
+    if (input.search) {
+      const term = `%${input.search}%`;
+      conditions.push(
+        or(
+          ilike(materiDocumentsTable.title, term),
+          ilike(materiDocumentsTable.content, term),
+        ),
+      );
+    }
+
+    // Category filter
+    if (input.category) {
+      conditions.push(eq(materiDocumentsTable.category, input.category));
+    }
+
+    // Owner filter
+    if (input.ownerId) {
+      conditions.push(eq(materiDocumentsTable.owner_user_id, input.ownerId));
+    }
+
+    // Only public (if requested)
+    if (input.onlyPublic) {
+      conditions.push(eq(materiDocumentsTable.is_public, true));
+    }
+
+    const whereClause =
+      conditions.length > 0 ? and(...conditions) : undefined;
+
+    const result = await db
+      .select()
+      .from(materiDocumentsTable)
+      .where(whereClause)
+      .orderBy(desc(materiDocumentsTable.created_at))
+      .limit(input.limit);
+
+    return result;
+  }
+
+  /** Get a single materi by id. */
+  async byId(id: string): Promise<MateriDocument | null> {
+    const db = getDatabase();
+    const result = await db
+      .select()
+      .from(materiDocumentsTable)
+      .where(eq(materiDocumentsTable.id, id))
+      .limit(1);
+    return result[0] ?? null;
+  }
+
+  /** Create a new materi document. */
+  async create(data: {
+    title: string;
+    description?: string | null;
+    content: string;
+    category: string;
+    tags: string[];
+    ownerUserId: string;
+    guildId?: string | null;
+    channelId?: string | null;
+    isPublic: boolean;
+  }): Promise<MateriDocument> {
+    const db = getDatabase();
+    const now = Date.now();
+    const result = await db
+      .insert(materiDocumentsTable)
+      .values({
+        title: data.title,
+        description: data.description ?? null,
+        content: data.content,
+        category: data.category,
+        tags: data.tags,
+        owner_user_id: data.ownerUserId,
+        guild_id: data.guildId ?? null,
+        channel_id: data.channelId ?? null,
+        is_public: data.isPublic,
+        view_count: 0,
+        created_at: now,
+        updated_at: now,
+      })
+      .returning();
+    return result[0]!;
+  }
+
+  /** Update an existing materi. */
+  async update(
+    id: string,
+    data: Partial<{
+      title: string;
+      description?: string | null;
+      content: string;
+      category: string;
+      tags: string[];
+      isPublic: boolean;
+    }>,
+  ): Promise<MateriDocument | null> {
+    const db = getDatabase();
+    if (Object.keys(data).length === 0) return this.byId(id);
+
+    const result = await db
+      .update(materiDocumentsTable)
+      .set({
+        ...data,
+        updated_at: Date.now(),
+      })
+      .where(eq(materiDocumentsTable.id, id))
+      .returning();
+    return result[0] ?? null;
+  }
+
+  /** Delete a materi. */
+  async delete(id: string): Promise<boolean> {
+    const db = getDatabase();
+    const result = await db
+      .delete(materiDocumentsTable)
+      .where(eq(materiDocumentsTable.id, id))
+      .returning({ deletedId: materiDocumentsTable.id });
+    return result.length > 0;
+  }
+
+  /** Increment view count (for analytics). */
+  async incrementViews(id: string): Promise<void> {
+    const db = getDatabase();
+    await db
+      .update(materiDocumentsTable)
+      .set({
+        view_count: sql`${materiDocumentsTable.view_count} + 1`,
+      })
+      .where(eq(materiDocumentsTable.id, id));
+  }
+}
+
+export const materiRepository = new MateriRepository();