Add End-to-End Integration Testing

Test full system integration end-to-end.

**Tasks:**
- [ ] Implement the feature
- [ ] Add comprehensive tests
- [ ] Update documentation
- [ ] Verify integration
- [ ] **Smart Contract - IP Registry:** 0 issues
- [ ] **Smart Contract - Atomic Swap:** 10 issues
- [ ] **API Server:** 20 issues
- [ ] **Testing & Infrastructure:** 17 issues

**Priority:** High