feat: add AgentCore Runtime entrypoint and deployment docs

- main.py with /invocations POST + /ping GET (AgentCore contract)
- Auto-detect mode from natural language prompt (analyze/review/fix)
- Delegates to existing orchestrator and AI agent
- agentcore/agentcore.json runtime configuration
- Full step-by-step docs: local testing, agentcore deploy, invoke, cleanup
- Local running docs (thothctl serve, uvicorn, ollama offline)
- CI/CD examples for GitHub Actions and Azure DevOps
- 20 unit tests covering endpoints, dispatch, and mode detection

Bumps version to 0.13.3

Author: Alejandro Velez