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/helicopter.svg

@@ -1,12 +1,29 @@
 <?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"/>
+    <!-- Main rotor disc (animated feel) -->
+    <ellipse cx="0" cy="-2" rx="11" ry="1" fill="currentColor" opacity="0.2"/>
+    <path d="M-11,-2 L11,-2" stroke="currentColor" stroke-width="0.5" opacity="0.4"/>
+    <path d="M0,-13 L0,9" stroke="currentColor" stroke-width="0.5" opacity="0.4"/>
+    
+    <!-- Main fuselage -->
+    <path d="M0,-8 C-3,-8 -4,-6 -4,-3 L-4,4 C-4,6 -3,7 -1,7 L1,7 C3,7 4,6 4,4 L4,-3 C4,-6 3,-8 0,-8 Z" fill="currentColor"/>
+    
+    <!-- Cockpit windscreen -->
+    <path d="M0,-8 C-2,-8 -3,-7 -3,-5 L-3,-3 L3,-3 L3,-5 C3,-7 2,-8 0,-8 Z" fill="currentColor" opacity="0.7"/>
+    
+    <!-- Tail boom -->
+    <rect x="-1" y="6" width="2" height="8" fill="currentColor"/>
+    
+    <!-- Tail rotor -->
+    <ellipse cx="0" cy="13" rx="1" ry="3" fill="currentColor"/>
+    <path d="M-3,13 L3,13" stroke="currentColor" stroke-width="0.8"/>
+    
+    <!-- Landing skids -->
+    <path d="M-3,7 L-3,9 L-1,9" stroke="currentColor" stroke-width="1" fill="none"/>
+    <path d="M3,7 L3,9 L1,9" stroke="currentColor" stroke-width="1" fill="none"/>
+    
+    <!-- Rotor hub -->
+    <circle cx="0" cy="-2" r="1" fill="currentColor"/>
   </g>
 </svg>