feat: dynamic agent persistence via MinIO + PostgreSQL

[Kaiohz]

Summary

• Store agent YAML configs in MinIO (object storage) with metadata indexed in PostgreSQL
• CRUD API endpoints (POST/PUT/DELETE/GET) for runtime agent management via multipart file upload
• Built-in agents from agents/ dir seeded on startup, protected from modification/deletion
• New hexagonal ports: AgentConfigStore, AgentConfigRepository
• New adapters: MinioAgentConfigStore, PostgresAgentConfigRepository, PersistentAgentRegistry
• Input validation: agent name regex, file size limit (1MB), UTF-8 check, YAML schema validation, name mismatch detection
• Persistence guard: CRUD endpoints return 503 if MinIO/PostgreSQL unavailable

Test plan

• 222 unit tests passing (42 new)
• Ruff: 0 issues
• SonarQube: 0 issues, 89.5% coverage (84.4% new code)
• Trivy: 0 vulnerabilities
• E2E QA: 22/22 test cases passing (health, CRUD, seeding, protection, edge cases)
• Docker Compose stack tested with MinIO + PostgreSQL connectivity

🤖 Generated with Claude Code