GitLab

- Add account_cost column to dashboard aggregation tables (migration 107)
- DashboardStats: add TotalAccountCost/TodayAccountCost fields
- ModelStat/GroupStat: add AccountCost field with SQL aggregation
- GetStatsWithFilters: always return TotalAccountCost (remove accountID filter)
- Dashboard Token cards: show user(green)/cost(orange)/standard(gray)
- Usage stats card: show account cost and standard below main value
- Model/Group distribution tables: add orange cost column

将 dashboard_aggregation_repo.go 和 usage_log_repo.go 中的时区处理
从 UTC 改为使用服务器配置时区（默认 Asia/Shanghai），确保"今日"
统计数据与用户预期一致。
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>