Implement Soroban Route Eligibility Rules Framework

# 🧠 Concept
Support configurable eligibility rules for routes.

## ⚠️ Problem
Route restrictions vary across integrations.

## 📁 Implementation Scope
- `src/rules/routes/stellar/`

## ✅ Requirements
- Define route rules
- Evaluate route eligibility
- Support custom rule extensions

## 🎯 Acceptance Criteria
- [ ] Eligibility framework implemented
- [ ] Rules applied successfully