Resolves #95

📝 Summary

This PR implements comprehensive RTL support for markmap, enabling proper rendering of RTL languages like Arabic, Hebrew, and Persian, as requested in issue #95.

✨ Key Features

• RTL Layout Engine: Complete coordinate transformation for right-to-left flow
• Line Continuity Fix: Resolved broken connecting lines in RTL mode
• Configuration Option: Added rtl: true/false in markmap options and frontmatter
• CSS Styling: Proper text direction and alignment for RTL content
• Type Safety: Full TypeScript interfaces and type definitions
• Backward Compatibility: RTL defaults to false, no breaking changes

🧪 Testing

• 30 tests passing (including 11 new RTL-specific tests)
• Real-world content: Tested with Arabic and Persian examples
• Interactive features: Zoom, pan, expand/collapse all working
• Code quality: ESLint and Prettier compliant

📋 Usage Example

---
markmap:
  rtl: true
---
# Arabic Example / مثال عربي
## Features / الميزات  
- RTL Layout / تخطيط من اليمين إلى اليسار
- Continuous Lines / خطوط متواصلة