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/shared/database/schema.ts

@@ -596,3 +596,44 @@ export type DbRetentionPolicyInsert =
 // Chatbot Messages
 export type ChatbotMessage = typeof chatbotMessagesTable.$inferSelect;
 export type ChatbotMessageInsert = typeof chatbotMessagesTable.$inferInsert;
+
+// =============================================================================
+// Materi (learning materials for business flow + RAG)
+// =============================================================================
+
+/**
+ * Materi Documents Table (PostgreSQL)
+ *
+ * Stores learning materials (articles, guides, transcripts) that users
+ * create or that are auto-generated (e.g. AI conversation summaries).
+ * Used by the RAG chat agent to ground answers in authoritative content.
+ */
+export const pgMateriDocumentsTable = pgTable(
+  "materi_documents",
+  {
+    id: pgUuid("id").primaryKey().defaultRandom(),
+    title: pgText("title").notNull(),
+    description: pgText("description"),
+    content: pgText("content").notNull(),
+    category: pgText("category").notNull().default("general"),
+    tags: pgText("tags").array(),
+    owner_user_id: pgText("owner_user_id").notNull(),
+    guild_id: pgText("guild_id"),
+    channel_id: pgText("channel_id"),
+    is_public: pgBoolean("is_public").notNull().default(true),
+    view_count: pgInteger("view_count").notNull().default(0),
+    created_at: pgBigint("created_at", { mode: "number" }).notNull(),
+    updated_at: pgBigint("updated_at", { mode: "number" }).notNull(),
+  },
+  (table) => ({
+    categoryIdx: pgIndex("idx_materi_category").on(table.category),
+    ownerIdx: pgIndex("idx_materi_owner").on(table.owner_user_id),
+    guildIdx: pgIndex("idx_materi_guild").on(table.guild_id),
+    searchIdx: pgIndex("idx_materi_search").on(table.title, table.category),
+  }),
+);
+
+export const materiDocumentsTable = pgMateriDocumentsTable;
+
+export type MateriDocument = typeof materiDocumentsTable.$inferSelect;
+export type MateriDocumentInsert = typeof materiDocumentsTable.$inferInsert;