7. Add cross-contract call audit

[DeFiVC]

What: Audit all cross-contract calls for safety and efficiency.

Why: Cross-contract calls are complex. Audit ensures safety.

Scope: Review all env.invoke_contract calls. Verify error handling. Check response parsing. Optimize where possible.

Acceptance criteria:

• All calls are reviewed
• Error handling is verified
• Responses are parsed correctly
• Optimizations are applied

Technical context: All contract source files.

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