Adding a github workflow to publish to npm on merge

[kevwilliams]

This PR adds a github workflow that will publish to NPM on merge to main.

Flow:

1. Triggers on every push to main
2. Skips if the actor is github-actions[bot] (prevents infinite loop from the version bump commit)
3. Uses dorny/paths-filter to skip the publish job entirely if nothing in packages/datum-ui/** changed
4. Reads the merged PR's labels to determine bump type — release:major, release:minor, or patch (default)
5. Runs npm version patch/minor/major inside packages/datum-ui/, which commits + tags
6. Pushes the tag back to main
7. Builds with pnpm --filter @datum-cloud/datum-ui build
8. Publishes with pnpm publish

No secret required, I will setup the NPM Trusted Publishing when this file is present in the repo.

To control the bump type, add a label to the PR before merging:

• release:major → major bump
• release:minor → minor bump
• no label → patch bump (default)

[scotwells]

@kevwilliams can we add this to the actions repo so we can share this across the organization?

[kevwilliams]

@kevwilliams can we add this to the actions repo so we can share this across the organization?

@scotwells Done - Added you as a reviewer on datum-cloud/actions#39 and updated this to use that reusable action.