feat: implement processDomainConsultation main handler

- Add full conversation flow with session management
- Handle tool call execution
- Support __PASSTHROUGH__ and __SESSION_END__ markers
- Add hasDomainSession helper for routing
- Export executeDomainAction from domain-tool.ts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/tools/domain-tool.ts

@@ -470,7 +470,7 @@ async function callNamecheapApi(
 }
 
 // 도메인 작업 직접 실행 (Agent 없이 코드로 처리)
-async function executeDomainAction(
+export async function executeDomainAction(
   action: string,
   args: { domain?: string; nameservers?: string[]; tld?: string },
   allowedDomains: string[],