ci: add manual publish-to-npm workflow

[PAMulligan]

Why

claudius-chat-widget still isn't on npm. The release-please workflow only runs its npm-publish step the one time it first cuts a release (release_created), so:

• it already ran (and failed) for v1.6.0 with the old token, and
• re-running that job is a no-op — the GitHub release for 1.6.0 already exists, so the publish step is skipped.

There's no built-in way to replay that publish. This adds a small workflow_dispatch workflow so we can publish on demand using the NPM_TOKEN secret (with provenance) — to bootstrap the first release now, and to recover from any future failed release publish.

After merge

Trigger it from the Actions tab (or gh workflow run "Publish to npm"). It builds the widget and runs npm publish --provenance --access public.

Note: for the first publish the token in NPM_TOKEN must be able to create a new package — a classic Automation token, or a granular token with All packages + read/write. A granular token scoped to a specific (not-yet-existing) package can't create it.

🤖 Generated with Claude Code