Improve aircraft icons and add weight-based color coding

- Replaced simple geometric shapes with detailed, realistic SVG icons for all aircraft types
- Implemented color differentiation based on aircraft weight categories:
  * Light (<7000kg): Sky blue
  * Medium (7000-34000kg): Green
  * Large (34000-136000kg): Orange
  * Heavy (>136000kg): Red
- Created new icons for: commercial airliner, helicopter, cargo aircraft, general aviation, military fighter, ground vehicle
- Updated legend to reflect new weight-based categories
- Modified getAircraftColor() to assign colors based on aircraft category/weight

Closes #17

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

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

assets/static/icons/ga.svg

@@ -1,7 +1,27 @@
 <?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)">
-    <!-- Small general aviation aircraft -->
-    <path d="M0,-10 L-5,6 L-1,6 L0,10 L1,6 L5,6 Z" fill="currentColor"/>
+    <!-- Small general aviation aircraft (Cessna-style) -->
+    <!-- Fuselage -->
+    <path d="M0,-12 L-1,-10 L-1,6 L-0.5,8 L0,9 L0.5,8 L1,6 L1,-10 Z" fill="currentColor"/>
+    <!-- High wings (typical of GA aircraft) -->
+    <path d="M-1,-2 L-10,0 L-10,1.5 L-1,0 Z" fill="currentColor"/>
+    <path d="M1,-2 L10,0 L10,1.5 L1,0 Z" fill="currentColor"/>
+    <!-- Wing struts -->
+    <path d="M-1,2 L-6,-1" stroke="currentColor" stroke-width="0.5"/>
+    <path d="M1,2 L6,-1" stroke="currentColor" stroke-width="0.5"/>
+    <!-- Tail wings -->
+    <path d="M-0.5,6 L-3.5,7.5 L-3.5,8.5 L-0.5,7.5 Z" fill="currentColor"/>
+    <path d="M0.5,6 L3.5,7.5 L3.5,8.5 L0.5,7.5 Z" fill="currentColor"/>
+    <!-- Vertical stabilizer -->
+    <path d="M0,5 L-0.4,5 L-1.5,9 L0,9 L1.5,9 L0.4,5 Z" fill="currentColor"/>
+    <!-- Propeller spinner -->
+    <circle cx="0" cy="-12" r="1.5" fill="currentColor"/>
+    <!-- Propeller blades -->
+    <path d="M-4,-12 L4,-12" stroke="currentColor" stroke-width="1" opacity="0.3"/>
+    <!-- Landing gear -->
+    <circle cx="-1" cy="5" r="0.8" fill="currentColor"/>
+    <circle cx="1" cy="5" r="0.8" fill="currentColor"/>
+    <circle cx="0" cy="-8" r="0.6" fill="currentColor"/>
   </g>
 </svg>