GitLab

- Cost cell: change gray "A $xxx" to orange "成本 $xxx" with i18n
- Remove standalone account_cost column from column settings (redundant)

- UserBreakdownItem: add AccountCost field + SQL aggregation
- UserBreakdownSubTable: add orange account cost column
- Admin usage table: add account_cost column (after cost, default visible)
- Column settings: add account_cost toggle option

- 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

Replace dead EventSource variable with AbortController to enable
cancelling fetch streams. Remove close-button disable during connecting
status so users can dismiss the dialog at any time.

- Show base amount (充值金额) as first line
- Show fee amount with percentage when fee_rate > 0
- Show pay_amount (实付金额) in bold primary color
- Show credited amount (到账金额) when different from pay_amount
- Compute baseAmount and feeAmount from backend order data

Backend:
- Validate recharge_fee_rate: 0 ≤ rate ≤ 100, max 2 decimal places

Frontend settings:
- Add % suffix icon to fee rate input
- Enforce max=100, min=0, step=0.01 with 2 decimal precision