ci: require static owned admission runner

[shtse8]

Summary

• replace the reusable ADR-29 admission workflow's dynamic runs-on expression with the literal sylphx-linux-standard profile
• remove the now-invalid caller-controlled runner input
• strengthen project-control so all central ADR-29 runner declarations must be literal static Linux profiles and dynamic selectors fail the gate

Compatibility evidence

• current GitHub code search found no repository calling adr29-admission.yml; the only references are central templates/docs/metadata, so no live caller relied on the removed input
• the template already declares four literal sylphx-linux-standard admission jobs

Local validation

• YAML parse of reusable workflow, template, and project-control workflow
• exact project-control runner-contract shell predicates
• no remaining inputs.runs-on or dynamic runs-on reference in tracked source
• node --check .github/actions/setup-changesets-publisher/changesets-publish.mjs
• git diff --check

Proof boundary

This changes GitHub-consumed reusable workflow source. The project-control PR run can prove the central static declaration and its ratchet; there is no current consumer invocation to claim as runtime proof.