Implement Soroban Contract Template Generator

# 🧠 Concept  
Generate secure starter templates for Soroban contracts.

## ⚠️ Problem  
Developers repeatedly recreate boilerplate setups.

## 📁 Implementation Scope  
- `packages/templates/stellar/`

## ✅ Requirements  
- Generate common contract templates  
- Include secure defaults  

## 🎯 Acceptance Criteria  
- [ ] Template generator implemented  
- [ ] Templates validated  