Switch to light map theme by default with dark mode toggle

Major improvements to map theming and aircraft type display:

Map Theme Changes:
- Changed default map from dark to light theme (CartoDB Positron)
- Added night mode toggle button with sun/moon icons
- Both main map and coverage map now switch themes together
- Light theme provides better daylight visibility

Aircraft Type Display:
- Now displays actual ADS-B category directly (e.g., "Medium 34000-136000kg")
- Removed guessing/interpretation of aircraft types
- Icons still use simplified categories for visual distinction
- More accurate and standards-compliant display

This provides a cleaner, more professional appearance with the light map
and gives users accurate ADS-B category information instead of interpreted types.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

assets/static/index.html

@@ -79,6 +79,7 @@
                     <button id="toggle-trails" title="Show/hide aircraft trails">Show Trails</button>
                     <button id="toggle-range" title="Show/hide range circles">Show Range</button>
                     <button id="toggle-sources" title="Show/hide source locations">Show Sources</button>
+                    <button id="toggle-dark-mode" title="Toggle dark/light mode">🌙 Night Mode</button>
                 </div>
                 
                 <!-- Legend -->