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/backend/src/shared/database/schema.ts

@@ -596,44 +596,3 @@ 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: pgJsonb("tags").notNull().default("[]"),
-    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;