feat: Add sanctions screening integration with on-chain verification

[nanaf6203-bit]

Description

Integrate with sanctions lists (OFAC, UN, EU) to screen addresses before allowing property transactions.

Acceptance Criteria

• Add SanctionsRegistry contract or module in compliance-registry
• Add screen_address(account) message returning ScreeningResult
• ScreeningResult: cleared, flagged, blocked with match details
• Integrate screening into property transfer flow
• Integrate screening into escrow creation flow
• Cache screening results with configurable TTL
• Add update_sanctions_list(merkle_root) admin message for efficient updates
• Emit AddressFlagged event when screening finds a match
• Test: flagged address cannot participate in property transfers