fix(ci): auto-publish release-please PRs without manual approval (#719)

The release PR (authored by github-actions[bot] via GITHUB_TOKEN) sat open
forever: its workflows were held behind 'awaiting approval' and the required
review could not be satisfied by the bot. Both release-please workflows now:

- Use a dedicated ${{ secrets.RELEASE_PLEASE_TOKEN }} (fine-grained PAT) with a
  GITHUB_TOKEN fallback. A PAT-authored PR runs CI automatically (no 'awaiting
  approval') and can be merged without a human.
- Auto-approve (as github-actions[bot], a different identity than the PR
  author) and enable auto-merge on the open release PR, so it publishes once
  checks pass. Skipped when no PAT is configured — falls back to today's manual
  flow, nothing breaks.

A PAT also un-suppresses the tag-push and release-published triggers on
docker-build (GITHUB_TOKEN suppressed them), so add a concurrency group there
to collapse the duplicate same-version builds into one.

Requires (repo/org settings, one-time):
- Create fine-grained PAT RELEASE_PLEASE_TOKEN (contents:write, pull-requests:write).
- Enable 'Allow auto-merge' on the repo (currently off).
- 'Allow GitHub Actions to approve pull requests' — already enabled.

.github/workflows/release-please.yml

@@ -20,10 +20,33 @@ jobs:
         uses: googleapis/release-please-action@v4
         id: release
         with:
-          token: ${{ secrets.GITHUB_TOKEN }}
+          # Dedicated token so the release PR runs CI + can auto-merge without a
+          # manual review. Falls back to GITHUB_TOKEN before the secret is set (#719).
+          token: ${{ secrets.RELEASE_PLEASE_TOKEN || secrets.GITHUB_TOKEN }}
           config-file: release-please-config.json
           manifest-file: .release-please-manifest.json
 
+      # Auto-approve + auto-merge the open stable release PR. See the beta
+      # workflow for the full rationale. Skipped on the release-cutting run and
+      # whenever no PAT is configured.
+      - name: Auto-approve and enable auto-merge on the release PR
+        if: ${{ steps.release.outputs.release_created != 'true' }}
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          RELEASE_PAT: ${{ secrets.RELEASE_PLEASE_TOKEN }}
+        run: |
+          if [ -z "$RELEASE_PAT" ]; then
+            echo "RELEASE_PLEASE_TOKEN not set — skipping auto-merge (manual review still required)."
+            exit 0
+          fi
+          pr=$(gh pr list --head release-please--branches--stable --state open --json number --jq '.[0].number // empty')
+          if [ -n "$pr" ]; then
+            gh pr review "$pr" --approve --body "Automated approval — release-please version bump + changelog (#719)." || true
+            gh pr merge "$pr" --squash --auto || true
+          else
+            echo "No open release PR to auto-merge."
+          fi
+
       - name: Output Release Info
         if: ${{ steps.release.outputs.release_created }}
         run: |