# Change: Update fund-summary username filter and shared summary card display

## Why

The frontend originally sent the current agent username through the `shop_name` query parameter when calling `GET /api/admin/shops/fund-summary`, which no longer matched the backend contract. That response also includes `main_balance`, which must be shown in both the agent home page and commission center withdrawable-commission cards.

The two withdrawable-commission cards are also duplicated between the home page and commission center. The home page currently renders an extra inline `佣金中心` chip inside the card header, which the product no longer wants. The two pages should render the same summary card through one shared component.

## What Changes

- Update the frontend contract for `GET /api/admin/shops/fund-summary` so self-scoped requests send the logged-in agent username under `username`, not `shop_name`
- Keep the query value unchanged; only the parameter name changes
- Show the backend `main_balance` field in the agent home page and commission center withdrawable-commission cards with the label `预充值余额`
- Preserve the existing amount formatting and empty-state behavior for the summary cards
- Remove the extra inline `佣金中心` text-and-chevron chip from the home-page withdrawable-commission card
- Standardize the home page and commission center withdrawable-commission cards behind one shared component so the visible summary structure stays aligned
- Remove the extra decorative icon wrapper so the summary icon is not rendered inside a separate boxed container

## Impact

- Affected specs:
  - `agent-fund-summary`
- Affected code:
  - `src/api/commission.ts`
  - shared fund-summary card component to be introduced for agent pages
  - `src/pages/agent-system/home/index.vue`
  - `src/pages/agent-system/commission-center/index.vue`
  - `src/pages/agent-system/withdraw/index.vue`
