feat: add Execute v1 public contract

[abrichr]

Summary

Adds the portable OpenAdapt Execute v1 trust contract to the MIT shared-schema package.

• Versioned async execution request, lifecycle, terminal outcome, and receipt schemas.
• Named EffectStrengthV1; separate waiting_for_reconciliation state and reconciliation_required outcome.
• rolled_back_verified only when independent compensation proof is present.
• Signed state, terminal, and attended-decision webhook envelopes.
• Generated OpenAPI 3.1 document at openadapt_types/schemas/execute-v1-openapi.json.

Boundary

This PR defines only open interfaces. It contains no Cloud implementation, tenanting, connector recipe, customer evidence, or deployment tuning.

Release coordination

This PR is intentionally draft. It layers alongside Types PR #19 and must join the coordinated Types 0.7 release only after Flow, Cloud, and Desktop consumer integration is ready.

Validation

• pytest -q (238 passed)
• scripts/export_control_overlay_schemas.py
• scripts/check_source_boundary.py --require-dist after building wheel and sdist

[abrichr]

Superseded by #21, which combined this Execute v1 contract with the reconciliation contract and regenerated the shared schema. The coordinated result is now published as openadapt-types 0.7.0.