Add Integration Tests for Cross-Contract Scenarios

## Overview
Add integration tests that verify contracts working together end-to-end.

## Background
Currently, only unit tests exist. Integration tests are needed to verify:
- Contract deployment order
- Cross-contract communication
- End-to-end workflows (payment → entitlement → policy evaluation)

## Tasks
- [ ] Set up drink! or similar integration test framework
- [ ] Write tests for contract deployment
- [ ] Test cross-contract call scenarios
- [ ] Test full payment-to-entitlement-to-access workflow
- [ ] Test error handling across contract boundaries
- [ ] Measure gas costs for composite operations
- [ ] Add CI/CD integration

## Related
- Code review finding: m7

## Priority
MINOR - Testing infrastructure

## Estimated Effort
3-4 days

Start by locating the existing unit tests and the contract deployment and cross-contract call entry points. Evaluate drink! or a similar integration framework, then define coverage for deployment order, payment-to-entitlement-to-policy workflows, boundary errors, composite gas costs, and CI/CD; done means these scenarios run end to end.

Written by the indexing model from the issue text.