Implement Soroban Contract Entrypoint Analyzer

# 🧠 Concept  
Analyze contract entrypoints and invocation paths.

## ⚠️ Problem  
Developers lack visibility into exposed contract interfaces.

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

## ✅ Requirements  
- Detect public entrypoints  
- Map invocation paths  

## 🎯 Acceptance Criteria  
- [ ] Entrypoints analyzed  
- [ ] Invocation paths reported  