Implement Open Source edition limits and feature restrictions

- Add 5 mutation types (paraphrase, noise, tone_shift, prompt_injection, custom)
- Cap mutations at 50 per test run
- Force sequential execution only
- Disable GitHub Actions integration (Cloud feature)
- Add upgrade prompts throughout CLI
- Update README with feature comparison
- Add limits.py module for centralized limit management
- Add cloud and limits CLI commands
- Update all documentation with Cloud upgrade messaging

examples/broken_agent/README.md

@@ -45,4 +45,3 @@ Try modifying `agent.py` to:
 4. Detect and refuse prompt injections
 
 Then re-run Entropix to see your robustness score improve!
-