docs: align AGENTS.md and ARCHITECTURE.md with actual implementation

- Add Observability, CLI, Skills sections
- Fix MCP tool I/O schemas to match actual Zod schemas
- Document all 4 LLM providers, 3 calibration methods, 8 cost models
- Add testing infrastructure, deployment (6 platforms), Docker details
- Remove non-existent file references and stale APIs
- Expand CI integration, gate presets, programmatic APIs
- Add skills directory reference and observability section

Author: reaatech