ci(release-please): use a PAT so releases trigger the publish workflows (#1920)

## Description

Makes the release pipeline hands-off by fixing the token release-please
uses.

### Why the current setup silently breaks publishing
release-please authenticates with `secrets.GITHUB_TOKEN`. **A
release/tag created by `GITHUB_TOKEN` does not emit events that trigger
other workflows** — this is GitHub's built-in recursion guard. So
`release.yml` (PyPI + npm) and `docker.yml`, which both fire on
`release: published`, **never ran off a bot-created release**. The
result: releases had to be cut by hand (`gh release create`, which runs
as a real user and *does* trigger them), and pip / npm / Docker drifted
out of sync (pip 0.30 vs Docker 0.27).

Proof: creating v0.31.0 manually (my user token) immediately kicked off
both `Release: v0.31.0` and `Docker: v0.31.0`; a `GITHUB_TOKEN`-created
release would not have.

### Change
Use `RELEASE_PLEASE_TOKEN` (a fine-grained PAT with `contents: write` +
`pull-requests: write`, treated by GitHub as a real user):
```yaml
token: ${{ secrets.RELEASE_PLEASE_TOKEN || secrets.GITHUB_TOKEN }}
```
- The release the bot creates now **does** trigger `release.yml` /
`docker.yml` → PyPI + npm + Docker publish automatically on merge of the
release PR.
- The PAT can also tag past branch/tag protection.
- Falls back to `GITHUB_TOKEN` if the secret is ever unset — the release
PR still opens; it just won't trigger downstream publishes (i.e. no
worse than today).

The `RELEASE_PLEASE_TOKEN` secret is already configured in repo
settings.

## Type of Change

- [x] Bug fix (non-breaking change that fixes an issue)
- [ ] New feature
- [ ] Breaking change
- [ ] Documentation update
- [ ] Performance improvement
- [ ] Code refactoring (no functional changes)

## Changes Made

- `.github/workflows/release-please.yml`: swap `token: ${{
secrets.GITHUB_TOKEN }}` for `${{ secrets.RELEASE_PLEASE_TOKEN ||
secrets.GITHUB_TOKEN }}`, with a comment explaining the recursion-guard
reason.

## Testing

- [x] Manual testing performed (YAML validated; token expression
resolves)

### Test Output

```text
$ python -c "import yaml; ... token: ${{ secrets.RELEASE_PLEASE_TOKEN || secrets.GITHUB_TOKEN }}"
parse OK
```

## Real Behavior Proof

- Environment: local macOS; CI workflow YAML change only.
- Exact command / steps: changed the `token:` input on the
`release-please-action` step to the PAT (with GITHUB_TOKEN fallback);
validated the workflow YAML parses and the token expression is correct.
- Observed result: the workflow now authenticates release-please as a
real user via `RELEASE_PLEASE_TOKEN`, so releases it creates will emit
`release: published` and trigger `release.yml` + `docker.yml`. Verified
out-of-band that a user-token release does trigger those two workflows
(v0.31.0), whereas the bot token does not.
- Not tested: a full bot-driven release cycle end-to-end (only
observable when the next release PR merges with this token in place);
this PR is the enabling change for that.

## Review Readiness

- [x] I have performed a self-review
- [x] This PR is ready for human review

## Checklist

- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] My changes generate no new warnings

.github/workflows/release-please.yml

@@ -44,6 +44,14 @@ jobs:
     steps:
       - uses: googleapis/release-please-action@v5
         with:
-          token: ${{ secrets.GITHUB_TOKEN }}
+          # PAT (not GITHUB_TOKEN): a release/tag created by GITHUB_TOKEN does
+          # NOT emit events that trigger other workflows, so release.yml
+          # (PyPI/npm) and docker.yml — which fire on `release: published` —
+          # never ran, and releases had to be cut by hand. A PAT is treated as a
+          # real user, so the release it creates DOES trigger those publishes; it
+          # also lets the bot tag past branch/tag protection. Falls back to
+          # GITHUB_TOKEN when the secret is unset (the release PR still opens; it
+          # just won't trigger the downstream publishes).
+          token: ${{ secrets.RELEASE_PLEASE_TOKEN || secrets.GITHUB_TOKEN }}
           config-file: .release-please-config.json
           manifest-file: .release-please-manifest.json