chore: add release workflow docs and scripts

[vibbyfs]

Summary

• document branching strategy and release flow
• add pull request template and linear history check workflow
• add release helper scripts and version marker

Testing

• npm test (fails: Missing script: "test")
• bash scripts/release/mark-main.sh (fails: This script must run on main. Current: work)

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https://chatgpt.com/codex/tasks/task_e_68afe672859c832b8af369376eee5230

[chatgpt-codex-connector]

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Reply with @codex fix comments to fix any unresolved comments.

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[chatgpt-codex-connector]

[P1] Linear history workflow flags every PR

The workflow checks for merge commits with git rev-list --merges origin/main..HEAD, but on pull_request events actions/checkout leaves HEAD on GitHub’s synthetic refs/pull/<id>/merge commit, which is itself a merge commit. As a result the check fails even when the head branch contains only rebased commits, blocking all releases to main. Consider checking origin/main..origin/${{ github.head_ref }} or checking out github.head_ref to avoid the synthetic merge.

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[chatgpt-codex-connector]

[P1] Release script never pushes marker commit

After merging development into main, the script runs mark-main.sh which creates a local commit bumping VERSION and CHANGELOG, but the script exits without pushing main back to origin. Every run will therefore leave the release marker only in the local clone and the remote branch stays unchanged, so the release history on GitHub is never updated.

Useful? React with 👍 / 👎.