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/cargo.svg

@@ -1,9 +1,28 @@
 <?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)">
-    <!-- Wide-body cargo aircraft shape -->
-    <path d="M0,-12 L-10,8 L-3,8 L0,12 L3,8 L10,8 Z" fill="currentColor"/>
-    <!-- Fuselage bulk -->
-    <rect x="-2" y="-6" width="4" height="8" fill="currentColor"/>
+    <!-- Wide-body cargo aircraft -->
+    <!-- Fuselage (wider) -->
+    <path d="M0,-14 L-2,-11 L-2,6 L-1.5,9 L0,10 L1.5,9 L2,6 L2,-11 Z" fill="currentColor"/>
+    <!-- Cargo door outline -->
+    <rect x="-1.5" y="-2" width="3" height="4" fill="none" stroke="currentColor" stroke-width="0.3" opacity="0.5"/>
+    <!-- Main wings (swept back more) -->
+    <path d="M-1.5,1 L-13,4 L-13,6 L-1.5,3.5 Z" fill="currentColor"/>
+    <path d="M1.5,1 L13,4 L13,6 L1.5,3.5 Z" fill="currentColor"/>
+    <!-- Winglets -->
+    <path d="M-13,4 L-13,2 L-12,4 Z" fill="currentColor"/>
+    <path d="M13,4 L13,2 L12,4 Z" fill="currentColor"/>
+    <!-- Tail wings (larger) -->
+    <path d="M-1,7 L-6,9 L-6,10 L-1,9 Z" fill="currentColor"/>
+    <path d="M1,7 L6,9 L6,10 L1,9 Z" fill="currentColor"/>
+    <!-- Vertical stabilizer (taller) -->
+    <path d="M0,5 L-0.7,5 L-3,10 L0,10 L3,10 L0.7,5 Z" fill="currentColor"/>
+    <!-- Nose cone (blunter for cargo) -->
+    <ellipse cx="0" cy="-13" rx="2" ry="2.5" fill="currentColor"/>
+    <!-- Engine nacelles (4 engines for heavy cargo) -->
+    <ellipse cx="-5" cy="2.5" rx="1.2" ry="2.2" fill="currentColor"/>
+    <ellipse cx="-8" cy="3" rx="1" ry="1.8" fill="currentColor"/>
+    <ellipse cx="5" cy="2.5" rx="1.2" ry="2.2" fill="currentColor"/>
+    <ellipse cx="8" cy="3" rx="1" ry="1.8" fill="currentColor"/>
   </g>
 </svg>