Feature: Contribution Mapping

New Contribution Mapping option in sidebar navigation Page structure with: Username input with validation Date range picker with validation Generate Contribution Map button Loading spinner state

Placeholders for team integration:

📈 Total Contributions section

🗓️ Heatmap section

🔍 Selected Day Details section

Session state setup for selected date handling

🎯 Purpose

This MR prepares the UI layout so that: Data/API team can plug in contribution data easily Visualization team can render heatmap and interactions