Extract aircraft SVG icons to external files and add dynamic marker updates

- Extract all aircraft type SVG designs to separate files in /static/icons/
- Add icon caching system with async loading and fallback mechanisms
- Implement dynamic marker icon updates when aircraft properties change
- Detect and respond to aircraft type/category, ground status, and rotation changes
- Use currentColor in SVG files for dynamic color application
- Maintain performance with intelligent change detection (5° rotation threshold)
- Support real-time marker updates for weight class transitions and ADS-B changes

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

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

assets/static/icons/ground.svg

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="32" height="32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg">
+  <g transform="translate(16,16)">
+    <!-- Ground vehicle - truck/car shape -->
+    <rect x="-6" y="-4" width="12" height="8" fill="currentColor" rx="2"/>
+    <!-- Wheels -->
+    <circle cx="-3" cy="2" r="2" fill="#333"/>
+    <circle cx="3" cy="2" r="2" fill="#333"/>
+  </g>
+</svg>