[M0] Upload durable CI evidence artifacts

[arthurpanhku]

Goal

Keep durable, traceable evidence for every CI decision.

Scope

Upload test, coverage, contract, audit/build, and evaluation outputs as GitHub Actions artifacts named with the workflow run ID and commit SHA.

Acceptance criteria

• Backend test and coverage reports are uploaded even when tests fail.
• Frontend test, production-audit, and build evidence is uploaded where applicable.
• OpenAPI contract and evaluation outputs are uploaded.
• Artifact names include workflow run ID and commit SHA.
• Retention and failure behavior are documented and avoid leaking secrets or source documents.
• A completed workflow run exposes all expected downloadable artifacts.