[BUG] AppAuthServiceImpl.updateDetail path appName uses first old path's appName (cross-link)

## Description
See the dedicated issue for `updateDetail`'s path appName handling — this entry is a tracking stub; the full detail is in the audit doc.

## Location
```
shenyu-admin/.../AppAuthServiceImpl.java:197-204
```

## Impact
Path appName silently lost/emptied.

## Suggested fix
Use `dto.getAppName()` per path.

## Related existing issue(s)
Covered by the updateDetail High issue above; grouped under Medium for visibility.

_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 by reading shenyu-admin/.../AppAuthServiceImpl.java lines 197-204 and consult docs/issue-candidates-2026-08-02.md for the full updateDetail context. Trace how each path is processed and verify that the completed behavior preserves the appName associated with its own DTO rather than an earlier path.

Written by the indexing model from the issue text.