refactor: consume public run artifact ability

[chubes4]

Summary

• replace direct Data Machine artifact and job-storage access with datamachine/get-run-artifacts
• preserve normalized artifacts, egress policy, and downstream PR/bundle behavior through one DMC-owned result contract
• distinguish unavailable integration, invalid job, missing run, unauthorized access, owner error, malformed response, valid empty, and populated results
• add architecture coverage preventing artifact-storage internals from returning

Verification

• php tests/run-artifact-public-ability.php
• php tests/run-artifact-repository-boundary.php
• php tests/run-artifact-architecture.php
• changed-file PHPCS and PHPStan level 7 via homeboy review lint --changed-only
• Homeboy architecture audit
• complete standalone tests/*.php suite: all pass except pre-existing bootstrap failure tracked in test: load GitCheckout in worktree cleanup patch equivalence smoke #1007
• WP-CLI workspace command registration and managed worktree show smokes

Depends on Data Machine PR Extra-Chill/data-machine#3060.

Closes #1006