feat: complete all 5 agent prompts for parallel execution

Added comprehensive prompts:
- prompts/agent-4-cloud-testing.md (1,400+ lines)
  - Unit tests for AWS/GCP/Azure scanners
  - Integration tests with mocked APIs
  - Test fixtures and helpers
  - 80%+ coverage target
  - Validates PR #39 cloud integration code

- prompts/agent-5-compliance.md (1,100+ lines)
  - SOC 2 (Service Organization Controls)
  - GDPR (EU data protection)
  - ISO 27001 (Info security management)
  - HIPAA (Healthcare data security)
  - Complete implementation examples
  - Testing and documentation requirements

All 5 agents now ready:
1. Agent 1: Event Streaming (3-5 days) ⭐ HIGH
2. Agent 2: REST API (4-6 days) ⭐ HIGH
3. Agent 3: Documentation (2-3 days) 📚 MEDIUM
4. Agent 4: Cloud Testing (3-4 days) 🧪 MEDIUM
5. Agent 5: Compliance Extended (3-4 days) 📋 LOW

Each prompt includes:
- Complete architecture and implementation details
- Step-by-step file creation guide
- Code examples and patterns
- Testing requirements
- Definition of done checklist
- Setup instructions

Total: ~6,000 lines of detailed agent instructions
Parallelism: All 5 can run simultaneously (only 1 minor conflict)
Timeline: 2 weeks to Phase 3 completion (60% → 100%)