fix(x-bots): X봇 생성 시 exclude_managed_channels ReferenceError 수정

POST body 스키마/구조분해에 exclude_managed_channels(default true,
컬럼 기본값과 일치)를 추가. 누락으로 INSERT 시 ReferenceError 크래시.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/routes/admin/x-bots.js

@@ -166,6 +166,7 @@ export default async function xBotsRoutes(fastify) {
           text_filters: { type: ['array', 'null'], items: { type: 'string' } },
           include_retweets: { type: 'boolean', default: false },
           extract_youtube: { type: 'boolean', default: false },
+          exclude_managed_channels: { type: 'boolean', default: true },
           cron_interval: { type: 'integer', default: 1 },
         },
         required: ['username'],
@@ -184,6 +185,7 @@ export default async function xBotsRoutes(fastify) {
       text_filters,
       include_retweets = false,
       extract_youtube = false,
+      exclude_managed_channels = true,
       cron_interval = 1,
     } = request.body;