fix(ux): no confirmation dialog when deleting a plugin from form

### Issue description

Clicking the **Delete** button on a plugin card inside a form (Routes, Services, Plugin Configs, etc.) immediately removes the plugin with no confirmation. There is no way to undo this — the user must re-add and re-configure the plugin from scratch.

**Current behavior**
`onDelete?.(name)` is called directly in `onClick` with no guard:
https://github.com/apache/apisix-dashboard/blob/master/src/components/form-slice/FormItemPlugins/PluginCard.tsx#L81

### Expected behavior

A confirmation dialog should appear before deleting, consistent with how top-level resources are deleted (`DeleteResourceBtn` uses `modals.openConfirmModal`).

### How to Reproduce

1. Go to Plugin Configs → Add Plugin Config
2. Add any plugin (e.g. `response-rewrite`) and configure it
3. Click **Delete** on the plugin card
4. Plugin is deleted instantly — no confirmation dialog

### Screenshots

https://github.com/user-attachments/assets/fd77cc89-46cc-42dd-a3d5-61e9e194cc3e

### Environment

- apisix-dashboard: master

### Additional context

_No response_

Start in src/components/form-slice/FormItemPlugins/PluginCard.tsx around the onClick handler at line 81, then compare the confirmation behavior in DeleteResourceBtn and its use of modals.openConfirmModal. The change is complete when deleting a plugin requires confirmation before onDelete is called; review the linked pull request for work already in progress.

Written by the indexing model from the issue text.