Implement Soroban Security Hotspot Detection

# 🧠 Concept  
Highlight high-risk areas within Soroban contracts.

## ⚠️ Problem  
Auditors spend significant time locating critical sections.

## 📁 Implementation Scope  
- `src/analysis/stellar/hotspots/`

## ✅ Requirements  
- Score risky functions  
- Highlight security-sensitive code  

## 🎯 Acceptance Criteria  
- [ ] Security hotspots detected  
- [ ] Hotspot scores generated  