Add Maps section with ArcGIS Online iframe integration

[evulins]

Description

Adds a new Maps section to the navigation with three map pages (Tree Density, Fragmentation, and Minimum Winter Temperature) that display ArcGIS Online maps via iframes. Refactors map pages from interactive Mapbox maps to embedded iframes, removing the need for admin upload functionality.

Type of Change

• New feature
• Bug fix
• Breaking change
• Documentation update

Changes Made

New Features

• Added "Maps" dropdown to main navigation with three sub-pages
• Created Maps landing page with thumbnail cards (similar to Data/Explainers pages)
• Added three map pages:
  • Tree Density
  • Fragmentation
  • Minimum Winter Temperature
• Each map page displays an ArcGIS Online iframe with placeholder URLs ready for configuration

Styling

• Applied consistent page header styling matching other pages (Download Data, Methodology, etc.)
• Implemented responsive iframe containers with proper spacing and shadows
• Used global .page-header styles from main.scss for consistency

Checklist

• Code follows project style guidelines
• No linting errors
• Components use consistent styling patterns
• Unit/integration tests (if applicable)
• Documentation (README updated if needed)

Technical Notes

• Iframe URLs are currently placeholders (IFRAME_URL = '') and should be updated with actual ArcGIS Online embed URLs
• All three map pages use the same layout structure for consistency
• Admin upload functionality has been completely removed as maps will be managed directly in ArcGIS Online

Tickets

• Issue Number - Add Maps section with ArcGIS Online integration

Screenshots

Please attach any design screenshots if UI update.