fix(db): migration 0013 rename mascot_chat_messages to chatbot_messages

/api/chat/history 500 (relation "chatbot_messages" does not exist):
codebase di-rename mascot->chatbot (977a6f9) tapi tabel DB tidak
pernah di-migrate — backend SELECT dari chatbot_messages, DB masih
mascot_chat_messages dengan kolom mascot_response.

- Migration 0013 (idempotent): ALTER TABLE mascot_chat_messages RENAME
  TO chatbot_messages, RENAME COLUMN mascot_response -> bot_response,
  RENAME INDEX -> idx_chatbot_messages_user_created; journal when >
  max(created_at) di __drizzle_migrations (0012)
- Diterapkan live via psql; riwayat chat lama tetap ada
- Verifikasi: GET /api/chat/history 200 + data, POST /api/chat 200
  + tersimpan (total history 1 -> 2)

services/discord-gateway/drizzle/migrations/0013_rename_mascot_chat_to_chatbot.sql

@@ -0,0 +1,19 @@
+-- Rename mascot chat tables/columns to chatbot (code rename in 977a6f9,
+-- DB was never migrated). Idempotent: no-ops on databases that already
+-- carry the new names (e.g. after a manual hotfix).
+ALTER TABLE IF EXISTS "mascot_chat_messages" RENAME TO "chatbot_messages";
+
+--> statement-breakpoint
+DO $$
+BEGIN
+  IF EXISTS (
+    SELECT 1
+    FROM information_schema.columns
+    WHERE table_name = 'chatbot_messages' AND column_name = 'mascot_response'
+  ) THEN
+    ALTER TABLE "chatbot_messages" RENAME COLUMN "mascot_response" TO "bot_response";
+  END IF;
+END $$;
+
+--> statement-breakpoint
+ALTER INDEX IF EXISTS "idx_mascot_chat_messages_user_created" RENAME TO "idx_chatbot_messages_user_created";

services/discord-gateway/drizzle/migrations/meta/_journal.json

@@ -92,6 +92,13 @@
       "when": 1785500000000,
       "tag": "0012_add_embedding_to_text_cache",
       "breakpoints": true
+    },
+    {
+      "idx": 13,
+      "version": "7",
+      "when": 1785551832190,
+      "tag": "0013_rename_mascot_chat_to_chatbot",
+      "breakpoints": true
     }
   ]
 }