Implement transponder code (squawk) lookup and textual descriptions

Resolves #30

- Add comprehensive squawk code lookup database with emergency, standard, military, and special codes
- Implement squawk.Database with 20+ common transponder codes including:
  * Emergency codes: 7700 (General Emergency), 7600 (Radio Failure), 7500 (Hijacking)
  * Standard codes: 1200/7000 (VFR), operational codes by region
  * Special codes: 1277 (SAR), 1255 (Fire Fighting), military codes
- Add SquawkDescription field to Aircraft struct and JSON marshaling
- Integrate squawk database into merger for automatic description population
- Update frontend with color-coded squawk display and tooltips:
  * Red for emergency codes with warning symbols
  * Orange for special operations
  * Gray for military codes
  * Green for standard operational codes
- Add comprehensive test coverage for squawk lookup functionality

Features:
- Visual emergency code identification for safety
- Educational descriptions for aviation enthusiasts
- Configurable lookup system for regional variations
- Hover tooltips with full code explanations
- Graceful fallback for unknown codes

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

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

assets/static/css/style.css

@@ -679,4 +679,62 @@ body {
     #aircraft-table td {
         padding: 0.5rem 0.25rem;
     }
+}
+
+/* Squawk Code Styling */
+.squawk-emergency {
+    background: #dc3545;
+    color: white;
+    padding: 2px 6px;
+    border-radius: 4px;
+    font-weight: bold;
+    cursor: help;
+    border: 1px solid #b52532;
+}
+
+.squawk-special {
+    background: #fd7e14;
+    color: white;
+    padding: 2px 6px;
+    border-radius: 4px;
+    font-weight: 500;
+    cursor: help;
+    border: 1px solid #e06911;
+}
+
+.squawk-military {
+    background: #6c757d;
+    color: white;
+    padding: 2px 6px;
+    border-radius: 4px;
+    font-weight: 500;
+    cursor: help;
+    border: 1px solid #565e64;
+}
+
+.squawk-standard {
+    background: #28a745;
+    color: white;
+    padding: 2px 6px;
+    border-radius: 4px;
+    font-weight: normal;
+    cursor: help;
+    border: 1px solid #1e7e34;
+}
+
+/* Hover effects for squawk codes */
+.squawk-emergency:hover {
+    background: #c82333;
+}
+
+.squawk-special:hover {
+    background: #e8590c;
+}
+
+.squawk-military:hover {
+    background: #5a6268;
+}
+
+.squawk-standard:hover {
+    background: #218838;
 }

assets/static/js/modules/ui-manager.js

@@ -122,7 +122,7 @@ export class UIManager {
         row.innerHTML = `
             <td><span class="type-badge ${type}">${icao}</span></td>
             <td>${aircraft.Callsign || '-'}</td>
-            <td>${aircraft.Squawk || '-'}</td>
+            <td>${this.formatSquawk(aircraft)}</td>
             <td>${altitude ? `${altitude} ft` : '-'}</td>
             <td>${aircraft.GroundSpeed || '-'} kt</td>
             <td>${distance ? distance.toFixed(1) : '-'} km</td>
@@ -180,6 +180,33 @@ export class UIManager {
         return 'signal-poor';
     }
 
+    formatSquawk(aircraft) {
+        if (!aircraft.Squawk) return '-';
+        
+        // If we have a description, format it nicely
+        if (aircraft.SquawkDescription) {
+            // Check if it's an emergency code (contains warning emoji)
+            if (aircraft.SquawkDescription.includes('⚠️')) {
+                return `<span class="squawk-emergency" title="${aircraft.SquawkDescription}">${aircraft.Squawk}</span>`;
+            }
+            // Check if it's a special code (contains special emoji)
+            else if (aircraft.SquawkDescription.includes('🔸')) {
+                return `<span class="squawk-special" title="${aircraft.SquawkDescription}">${aircraft.Squawk}</span>`;
+            }
+            // Check if it's a military code (contains military emoji)
+            else if (aircraft.SquawkDescription.includes('🔰')) {
+                return `<span class="squawk-military" title="${aircraft.SquawkDescription}">${aircraft.Squawk}</span>`;
+            }
+            // Standard codes
+            else {
+                return `<span class="squawk-standard" title="${aircraft.SquawkDescription}">${aircraft.Squawk}</span>`;
+            }
+        }
+        
+        // No description available, show just the code
+        return aircraft.Squawk;
+    }
+
     updateSourceFilter() {
         const select = document.getElementById('source-filter');
         if (!select) return;