ci: add sync workflow to merge release tags back to main

[designcode]

Summary

• Adds sync-release-to-main.yaml workflow that runs after each successful Release workflow on the release branch
• Automatically creates and merges a PR from release → main (merge commit) so release tags are reachable from main's history
• Fixes the root cause of beta versions being stuck — semantic-release on main couldn't see stable release tags because they lived on merge commits only reachable from release

How it works

1. Release workflow completes on release branch
2. Sync workflow triggers via workflow_run
3. Checks if release is ahead of main
4. Creates a PR release → main and auto-merges with merge commit

Test plan

• Validated on tigrisdata/semantic-release-test with the same branch model

🤖 Generated with Claude Code

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Note

Medium Risk
Adds an automated workflow that can create and merge PRs into main with write permissions; misconfiguration or unexpected release history could cause unintended merges.

Overview
Adds a new GitHub Actions workflow (sync-release-to-main.yaml) that triggers after a successful Release workflow run on the release branch.

When release is ahead of main, it uses the GitHub CLI to create (if needed) and auto-merge a release → main sync PR, ensuring release commits/tags are merged back into main history.

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[github-actions]

🎉 This PR is included in version 2.16.1 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

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