Gate property issuance on cross-chain identity verification

[nanaf6203-bit]

Problem Statement

Identity verification stubs exist but aren't enforced in register_property.

Why it matters

Compliance.

Technical Context

Add verify_onboarding_cross_chain that pulls KYC from foreign chain via XCM-style mock.

Expected Outcome

Onboarding requires remote attestation.

Acceptance Criteria

1. Tests cover both attested and unattested paths.
2. Kani harness.
3. SDK helper.
4. Docs.

Implementation Notes

Cross-contract call.

Files or modules likely to be affected

contracts/property-management/src/lib.rs.

Dependencies

#38.

Difficulty level

MEDIUM.

Estimated effort

M (~3 days).