ci: automate dist/ build and v1 tag release

[jackieli-tes]

Summary

• Issue Add build artifact to workflow #20: Build workflow now auto-commits dist/ artifacts on push to main — no more manual builds before pushing. On PRs, it just verifies the build succeeds.
• Issue 💡 - automate v1 compatible release #21: New release workflow automatically moves the major version tag (e.g. v1) when a v1.x.y release is published, replacing the manual git tag -f + git push -f --tags process.
• Test workflows now trigger via workflow_run after build completes on main, ensuring tests always use freshly built artifacts.
• Minor cleanups: fixed deprecated set-output syntax, updated GITHUB_OUTPUT usage.

Closes #20, closes #21

Test plan

• Push a source-only change to main and verify the build workflow auto-commits dist/
• Verify test workflows trigger after build completes (via workflow_run)
• Create a test release and verify the v1 tag is automatically moved
• Open a PR and verify the build step runs without auto-committing