Restore /snapit using workflow dispatch

[gonzaloriestra]

WHY are these changes introduced?

npm no longer allows Trusted Publishing from issue_comment workflow runs, so /snapit cannot publish snapshots directly.

WHAT is this pull request doing?

Keep /snapit by dispatching a separate release run on the default branch. The publisher checks the original comment, the requester's write permission, and the current PR commit before running pnpm release snapshot. Fork PRs remain unsupported. The snapit action is no longer used.

Report the installation command or failure on the PR. Existing manual and scheduled releases keep their current behavior. No new secrets or npm configuration are required.

How to manually test your changes?

Merge and /snapit

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add