ci(publish): run npm publish on GitHub-hosted runners

npm rejects provenance bundles from self-hosted runners (E422 after the
Blacksmith migration); the publish jobs go back to ubuntu-latest.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tGFyF841jinkhw1933Zwp

Author: sunnylqm

.github/workflows/publish.yml

@@ -9,7 +9,7 @@ permissions:
 
 jobs:
   build:
-    runs-on: blacksmith-4vcpu-ubuntu-2404
+    runs-on: ubuntu-latest  # npm --provenance requires a GitHub-hosted runner
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v6