Spec closure: standalone review and ship workflows

[ganesh47]

Close the active-spec gap by shipping first-class cstack review and cstack ship commands.

Scope:

• add CLI entrypoints
• extract or reuse deliver review/ship execution logic
• make artifacts inspectable in standalone runs
• add tests
• align README/spec/workflow docs

[ganesh47]

Shipped in 5d31e4a and released in v0.13.0.

Completed:

• added standalone cstack review <prompt> [--from-run <run-id>]
• added standalone cstack ship <prompt> [--from-run <run-id>] [--release] [--issue <n>] [--allow-dirty]
• implemented durable review artifacts: findings.md, findings.json, verdict.json
• implemented durable ship artifacts and GitHub evidence artifacts
• extended inspector support for standalone review/ship runs
• added regression coverage in test/review.test.ts and test/ship.test.ts

These workflows are now first-class commands rather than deliver-only internals.