[BUG] ApiBean.copy() back-references the original ApiBean, losing processor-applied beanPath

## Description
The copied `ApiDefinition`s are constructed with `new ApiDefinition(this, ...)` so each copy's `apiBean` field points back at the **original** `ApiBean`, not at `copy`. Registrars read the path via `api.getApiBean().getBeanPath()`, so a processor's `setBeanPath` on the copy is silently lost.

## Location
```
shenyu-client-core/.../register/ApiBean.java:245-254
MateDataApiRegistrarImpl.java:183-185, ApiDocRegistrarImpl.java:170-172
```

## Impact
A class-level path override set on the copy (e.g. `@ShenyuSpringMvcClient(path="/foo")` with no class `@RequestMapping`) is dropped from the registered path.

## Suggested fix
`new ApiDefinition(copy, definition.apiMethod, definition.methodPath)`.

## Related existing issue(s)
None

_Identified during the 2026-08-02 audit; full list in [`docs/issue-candidates-2026-08-02.md`](docs/issue-candidates-2026-08-02.md)._

Start in shenyu-client-core/.../register/ApiBean.java at lines 245-254, then inspect the ApiDefinition consumers in MateDataApiRegistrarImpl.java and ApiDocRegistrarImpl.java at the cited lines. Verify that copied definitions retain the copied ApiBean's processor-applied beanPath and that registration uses the overridden path.

Written by the indexing model from the issue text.