docs: audit, HF Spaces fix, and deep inline walkthrough comments

fix: revert max_new_tokens, improve error display, forbid comments in generated code

fix: increase token budget for long tasks and show all 4 example buttons

Phase 4 upgrades: fixes 10, 16, 18, 19

Fix JSON parse failure: raise token limits and add truncation salvage

Implement complete Self-Healing Code Agent framework