[Bug][DevLake] Project deletion lifecycle lacks extension hook for plugin-owned state

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/incubator-devlake/issues?q=is%3Aissue) and found no similar issues.

### What happened

The generic `DELETE /projects/:projectName` endpoint deletes a project through `services.DeleteProject()` without exposing a lifecycle hook for plugins or features that maintain project-scoped state.

Core DevLake records such as the project, blueprint, mappings and metric settings are cleaned up, but feature-owned records can be left stale if their cleanup normally happens through a feature-specific or Config UI deletion flow.

There is already a project lifecycle extension for renames through `ProjectService.RenameProject(...)`, but there is no equivalent hook for deletion.

### What do you expect to happen

Project deletion should provide a lifecycle extension point that allows plugins or features with project-scoped state to validate and clean up their own records before the project is deleted.

Ideally this should integrate with the core deletion transaction where possible so project deletion and feature-owned cleanup cannot leave inconsistent state.

For example, the existing `ProjectService` boundary could expose a `BeforeDeleteProject` or `DeleteProject` hook similar to `RenameProject`.

### How to reproduce

1. Add or use a feature/plugin that persists a record associated with a DevLake project and normally removes or validates that record during its own project-deletion flow.
2. Create a DevLake project and associate feature-owned state with it.
3. Delete the project directly through:

DELETE /projects/:projectName

4. Observe that `server/api/project.DeleteProject` calls `services.DeleteProject(projectName)` directly.
5. Observe that core project records are removed, but no plugin/feature deletion hook is invoked.
6. The feature-owned project association can therefore remain stale or orphaned.

This is reproducible on current `main` at commit:

f110addad86930c4c792a3d22051e922346f3656

### Anything else

_No response_

### Version

f110addad86930c4c792a3d22051e922346f3656

### Are you willing to submit PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)