ISSUE 04 — SUB ISSUE 06 — Citation Mirroring Feature

## 🧩 Mô tả
So sánh citation giữa external vs self citation.

## 🎯 Scope

- Dual line chart rendering
- Legend system
- Axis + grid layout
- Tooltip comparison 2 series
- Visual differentiation giữa 2 data sets

## 📦 Output Expected
- Chart comparison rõ ràng 2 trend

## ✅ Acceptance Criteria

- 2 lines hiển thị đúng data
- Legend map đúng series
- Tooltip show đúng values
- Không overlap UI