Fix release PR check triggering from workflow-created PRs

[EdwardIrby]

Context

The open-release-pr.yml workflow can create or update the dev -> main release PR using GITHUB_TOKEN.

On PR #293, the release PR was created successfully, but required test-pr stayed in Expected — Waiting for status to be reported because GitHub does not trigger most downstream workflows from GITHUB_TOKEN-authored events. Closing and reopening the PR manually triggered the expected pull_request checks.

Goal

Make release PR creation/update report required checks without requiring a manual close/reopen workaround.

Desired Outcome

A maintainer can run open-release-pr.yml and get a release PR that satisfies branch protection checks normally.

Scope

• Review .github/workflows/open-release-pr.yml.
• Decide whether to use a narrowly scoped maintainer PAT/GitHub App token for PR creation/update, or another safe approach that causes required PR checks to run.
• Preserve existing gates:
  • exactly one open release-readiness issue
  • ready: true
  • risk_level: none
  • current dev SHA in readiness issue
  • security facts available
  • final pending checks = 0
  • no auto-merge
  • no publish
• Keep dry-run behavior non-mutating.
• Keep permissions minimal.

Acceptance Criteria

• open-release-pr.yml can create or update dev -> main release PRs in a way that causes required pull_request checks like test-pr to report.
• The workflow documents the token source and why it is needed.
• If a PAT/App token is used, normal repo operations still use GITHUB_TOKEN where possible.
• No branch-mutating automation is added beyond opening/updating the release PR.
• No auto-merge or publish behavior is added.
• Validation includes a dry-run and a real run or a clearly justified equivalent smoke test.

Known Workaround

Manual close/reopen of the release PR triggers the required checks, but this should not be the durable release flow.

Refs #293.

[EdwardIrby]

Closing the current issue backlog while the repository resets the agent workflow and MSS slice plan.