feat: add semantic-release with conventional commits

[joris974]

Summary

• Add semantic-release configuration (.releaserc.yaml) with conventionalcommits preset, NPM publish, and GitHub release plugins
• Add release.yml workflow using cycjimmy/semantic-release-action@v6.0.0
• Support rc/* branches for pre-releases
• Add RELEASE.md with conventional commit instructions
• Add release section to README.md
• Uses pnpm for build command in .releaserc.yaml (matching this repo's package manager)

Prerequisites

Before merging, ensure:

• NPM_TOKEN secret is configured on the repo for NPM publishing
• Repository rulesets have a bypass configured for the release bot (if applicable)

Test plan

• Verify YAML syntax is valid for .releaserc.yaml and release.yml
• Confirm CI workflow passes on this PR
• After merge, verify a release is triggered with the feat: commit prefix
• Test pre-release flow by pushing to an rc/* branch

Mirrors freckle/i18n-scripts-js#21

[jleichty-ren]

this looks like the same release setup as freckle/cancelable-promise-js#152, so the main concerns were:

• the release config calls pnpm install && pnpm run build, but the release workflow doesn’t set up pnpm first
• @semantic-release/git runs before @semantic-release/npm, so i’m not sure the bumped package.json would get committed back
• if we do want to commit back to main, ${{ github.token }} may not be the right token for the repo ruleset
• it may be worth adding "files": ["dist"] before automated publishing