[CONTRACT] Add cross-shipment state consistency verification framework

[dinahmaccodes]

Tier: 🔴 Hard

Description:

Implement a framework for verifying consistency relationships between related shipments (e.g., batch-created shipments must maintain group invariants). Detects anomalies that could indicate state corruption or logic bugs.

Tasks:

• Define consistency rules for shipment relationships
• Create invariant checking functions
• Implement batch consistency verification
• Add admin query to detect consistency violations
• Create comprehensive test coverage

File locations:

• New consistency module → contracts/shipment/src/consistency.rs
• Integration in lib.rs → expose verification queries
• Tests → tests/test_consistency.rs

Acceptance Criteria:

• All batch relationships maintained
• Consistency violations detected reliably
• Admin can query and correct violations
• Tests verify detection of artificial inconsistencies
• No false positives in healthy state

PR Checklist:

• Consistency framework implemented
• All batch invariants verified
• Detection and correction procedures in place
• Tests cover all invariant types
• cargo test shows 100% pass rate

Reference: Read CONTRIBUTING.md before starting.