fix: close final promotion contract gaps

[BeforeLights]

Summary

• document the emitted membership rejection envelope in OpenAPI
• validate malformed orchestration handoff lists without throwing
• cover project-scope uniqueness normalization
• update the PR promote: IAM foundation reconciliation to main #40 CodeRabbit disposition with the automatic incremental result

Verification

• corepack pnpm --filter @databreeze/api test (342 passing)
• corepack pnpm repo:check
• corepack pnpm repo:build
• git diff --check

Focused promotion-gate fix for PR #40. CodeRabbit is not invoked on this dev PR; PR #40 already completed its permitted review flow and its integration emitted the recorded incremental result automatically.

[coderabbitai]

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