Switch release automation to branch-based versioning

[lklynet]

Summary

• Replaced commit-message-driven release flow with branch-based version resolution for main and test.
• Added shared version helpers so the app, frontend, and CI can resolve versions consistently from env vars, Git tags, or the current commit.
• Split release automation into validate, guard, version computation, image publish, tag creation, and GitHub Release steps.
• Removed commitlint, Husky commit hooks, and the old semantic-release/publish-image workflow in favor of the new release pipeline.
• Updated contributor guidance to reflect branch naming, commit message expectations, and CI-owned versioning.

Testing

• Added unit coverage for resolveAppVersion in .tests/helpers/app-version.test.js.
• Added unit coverage for resolveNextRelease in .tests/helpers/resolve-next-release.test.js.
• Not run: full test suite.
• Not run: GitHub Actions release workflow.
• Not run: Docker image build and publish pipeline.