fix(ci): use PAT for release please to trigger build workflow

[webbertakken]

Summary

• Use RELEASE_TOKEN (PAT) instead of default GITHUB_TOKEN in release-please workflow
• Tags created by the default token don't trigger other workflows (GitHub security measure)
• Using a PAT means the tag comes from a real user account, which triggers the build workflow

Setup required

1. Create a fine-grained PAT scoped to this repo with Contents: Read and write
2. Add it as repo secret RELEASE_TOKEN

Test plan

• Merge a release PR and verify the build workflow triggers automatically