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/helicopter.svg

@@ -0,0 +1,12 @@
+<?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)">
+    <!-- Rotor disc -->
+    <circle cx="0" cy="0" r="10" fill="none" stroke="currentColor" stroke-width="1" opacity="0.3"/>
+    <!-- Main body -->
+    <path d="M0,-8 L-6,6 L-1,6 L0,8 L1,6 L6,6 Z" fill="currentColor"/>
+    <!-- Rotor mast -->
+    <path d="M0,-6 L0,-10" stroke="currentColor" stroke-width="2"/>
+    <path d="M0,6 L0,8" stroke="currentColor" stroke-width="2"/>
+  </g>
+</svg>