[U29] Produce checksummed cross-platform CLI artifacts

[ZempTime]

PRD: #1
Delivery unit: U29
Campaign: C09
Canonical graph: https://github.com/ZempTime/shortbread/blob/246320c73d81e5afdf0490b43a2b02272f40268b/docs/initiatives/2026-07-shortbread-v1/05_delivery_replan/output/2026-07-20-delivery-plan.md
Common unit contract: https://github.com/ZempTime/shortbread/blob/246320c73d81e5afdf0490b43a2b02272f40268b/docs/initiatives/2026-07-shortbread-v1/05_delivery_replan/output/UNIT-CONTRACT.md

• Acceptance umbrella / blockers: GitHub Produce release-candidate application and CLI artifacts #12; blocked by U01, U08, U10, U11, U12, U23, U25, and U26.
• Outcome: Supported macOS/Linux users install a single shortbread binary, verify checksums, inspect version/commit/API range, and run the complete management command surface without a language runtime.
• Failure/recovery: Unsupported architecture, corrupt checksum, incompatible API, missing keyring, non-interactive misuse, and partial install fail with non-mutating instructions.
• Evidence: Cross-builds, checksums, dependency/SBOM inventory, clean-machine install probes, every black-box command/JSON contract, and supply-chain review.
• Central surfaces / impact: GoReleaser/build config, CLI version/command registry, artifact names/docs. No stable release tag yet.
• Safe split: Architecture builds may run as matrix jobs, but the unit promotes one consistent version/compatibility/checksum contract.

Every integration records a factory candidate with evidence or No reusable harvest.