Allow the npm publish workflow to be run manually

[MikeAlhayek]

Summary

Add a workflow_dispatch trigger to publish_npm_release.yml so a release can also be started from the Actions tab (Run workflow), alongside the existing tag trigger. This was meant to land with #20 but was pushed just after that PR merged.

• The manual run takes a required version input (e.g. 1.2.6, no leading v). It is used instead of the tag name and published from the branch selected in the dialog.
• The version, from either a tag or the input, must be MAJOR.MINOR.PATCH (a leading v is accepted).
• Tag pushes behave as before. A manual run publishes to npm but does not create a git tag.

The Run workflow button only appears once this is on main.

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