Wire test, docs, and report conventions into builder chain

[TheGreatAxios]

Summary

• Builder prompt and implement skill carry the same three strands: same-commit regression tests, same-commit docs upkeep, and criteria-mapped reporting with command evidence
• Contract test pins the prompt markers without pinning wording

Verification

• bun run lint, bun run typecheck, and bun run build pass
• bun test src/agent/directors/builder/ passes (21 tests, 0 fail)
• Full bun run test is not green: unrelated timing-sensitive tests fail with different sets on identical seeds (details in the branch report)

Fixes CL-6806

Sawyer review requested — do not merge

[linear-code]

CL-6806