CLI: add `modeldock verify --all`

[himanshu231204]

Background

verify works per-model but not for all at once.

Why it matters

Bulk integrity checks are useful after storage changes.

Acceptance criteria

• modeldock verify --all verifies every installed model.
• Prints a summary table.
• Reuse core/manager.py verify logic; add tests.

Where to look

• src/modeldock/cli/commands/, src/modeldock/core/manager.py

How to claim

Comment /claim on this issue.

[utkarsha741]

/claim

[github-actions]

🎉 Thanks @utkarsha741!

This issue has been assigned to you.

Happy coding! 🚀