feat(agent-office): AI 토큰 사용량 뱃지 표시

- api.js: getAgentTokenUsage 헬퍼 추가
- AgentColumn: 헤더에 오늘 토큰 사용량 뱃지 (🧮 N,NNN)
- 30초 폴링 + state 변경 시 즉시 갱신

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/api.js

@@ -599,4 +599,5 @@ export const sendAgentCommand  = (agent, action, params={}) => apiPost('/api/age
 export const approveAgentTask  = (agent, task_id, approved, feedback='') => apiPost('/api/agent-office/approve', { agent, task_id, approved, feedback });
 export const getAgentStates    = ()           => apiGet('/api/agent-office/states');
 export const getActivityFeed   = (limit=50, offset=0) => apiGet(`/api/agent-office/activity?limit=${limit}&offset=${offset}`);
+export const getAgentTokenUsage = (id, days=1) => apiGet(`/api/agent-office/agents/${id}/token-usage?days=${days}`);