[codex] smoke test built skill bundle

[bzcsk2]

What changed

• Extends scripts/verify.py to inspect dist/detectoracle.skill after build.
• Checks required bundle entries, packs content, and references content inside the archive.
• Extracts the built skill bundle to a temporary directory.
• Runs the public bundled entrypoint with:
  • detectoracle.py diagnose
  • detectoracle.py validate <extracted>/packs

Why

The previous verification primarily checked source-tree files and bundle entry presence. This PR adds a post-build smoke test so CI catches cases where the source tree works but the packaged .skill artifact cannot run after extraction.

Validation

Passed CI run #228 on the PR head commit.

The workflow completed successfully across the full matrix:

• Ubuntu latest / Python 3.12
• Ubuntu latest / Python 3.13
• Windows latest / Python 3.12
• Windows latest / Python 3.13

Each job passed format, lint, tests, built-in pack validation, evals, diagnose, build, and bundle verification. The bundle verification now includes extracting the built .skill artifact and running the bundled public entrypoint.