feat: Add AI Safety Rules (.cursor/rules) + Local Enforcer

[kwstx]

Hey! I've been using this starter with Cursor and finding it really helpful.

The Problem:
I noticed that when "Vibe Coding" quickly, the AI often hallucinates Next.js/Supabase patterns that are deprecated (e.g., using layout="fill" in next/image or hallucinated Tailwind classes).

The Fix:

1. I added a strict .cursor/rules/ai-regression-safety.mdc file to index these specific constraints for the AI.
2. I added use-engram.engram to the recommended extensions. It's a local tool that acts as a "Shadow Guard"—if the AI tries to break the safety rules defined above, Engram blocks it locally before save.

This makes the template much safer for people generating code rapidly with generic models.