Parallelize npm publishing with docs publishing

Previously, npm publishing only started after the entire main.yaml workflow
completed (including docs publishing) due to using workflow_run trigger.

Now, publish-npm job triggers build.yaml via workflow_dispatch immediately
after publish-jsr completes, allowing npm and docs publishing to run in
parallel.

Changes:

- Rename publish job to publish-jsr for clarity
- Add publish-npm job that triggers build.yaml via workflow_dispatch
- Remove workflow_run trigger from build.yaml (now solely workflow_dispatch)
- Update publish-docs dependency to publish-jsr

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>