[Code scan] Harden PyPI publish workflow trigger and OIDC permissions

This issue was found during a Codex global code scan of the repository.

Baseline commit: e3c5b38a99eb7ab778b5d8c68a5ed4ddf6cf91b3

Problem

The PyPI release workflow runs on every push and pull request, but grants `id-token: write` at the job level before the tag-only publish step. The publish condition also accepts any pushed tag name.

Code references:
https://github.com/deepmodeling/dpgui/blob/e3c5b38a99eb7ab778b5d8c68a5ed4ddf6cf91b3/.github/workflows/release.yml#L1-L17

Relevant snippet:
```yaml
on: [push, pull_request]
...
permissions:
id-token: write
...
if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags')
```

Impact

OIDC token minting permission is available to the whole job even for non-release events, and accidental tags such as `test-release` or `latest` would satisfy the publish gate. This increases the blast radius of the release workflow.

Suggested fix

Split build/test and publish into separate jobs. Give `id-token: write` only to a publish job with a job-level release condition, restrict triggers to version tags such as `v*` or `v[0-9]*`, and validate that the tag matches the package version before publishing.