Feature/super admin analytics dashboard

[sakshi-lily]

Summary

This PR redesigns the Super Admin "National Oversight" section by replacing the raw school data table with an analytics-focused dashboard.

Changes Made

• Removed the detailed school listing from the National Oversight section
• Added executive KPI cards for key nationwide metrics
• Introduced data visualizations and analytics for better decision-making
• Added school growth and performance insights
• Added interview and AI usage analytics
• Added engagement and system health metrics
• Improved dashboard layout, responsiveness, and overall user experience
• Preserved existing backend functionality and API integrations

Benefits

• Provides actionable insights instead of raw data
• Makes the dashboard more suitable for national-level monitoring
• Improves readability and user experience
• Supports faster decision-making through visual analytics

Testing

• Verified dashboard renders correctly
• Verified existing APIs continue to work
• Verified responsive layout across different screen sizes
• Confirmed no impact on existing functionality