Fix CPR zone ambiguity causing aircraft to appear 100km away from actual position

PROBLEM:
- Aircraft were appearing ~100km from receiver when actually ~5km away
- CPR (Compact Position Reporting) algorithm has zone ambiguity issue
- Without reference position, aircraft can appear in wrong 6-degree zones

SOLUTION:
- Add receiver reference position to CPR decoder for zone resolution
- Modified NewDecoder() to accept reference latitude/longitude parameters
- Implement distance-based zone selection (choose solution closest to receiver)
- Updated all decoder instantiations to pass receiver coordinates

TECHNICAL CHANGES:
- decoder.go: Add refLatitude/refLongitude fields and zone ambiguity resolution
- beast.go: Pass source coordinates to NewDecoder()
- beast-dump/main.go: Use default coordinates (0,0) for command-line tool
- merger.go: Add position update debugging for verification
- JavaScript: Add coordinate validation and update logging

RESULT:
- Aircraft now appear at correct distances from receiver
- CPR zone selection based on proximity to known receiver location
- Resolves fundamental ADS-B position accuracy issue

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

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

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

@@ -59,6 +59,7 @@ export class AircraftManager {
         
         // Debug: Log coordinate format and values
         console.log(`📍 ${icao}: pos=[${pos[0]}, ${pos[1]}], types=[${typeof pos[0]}, ${typeof pos[1]}]`);
+        console.log(`🔍 Marker check for ${icao}: has=${this.aircraftMarkers.has(icao)}, map_size=${this.aircraftMarkers.size}`);
         
         // Check for invalid coordinates - proper geographic bounds
         const isValidLat = pos[0] >= -90 && pos[0] <= 90;
@@ -74,6 +75,8 @@ export class AircraftManager {
             const marker = this.aircraftMarkers.get(icao);
             
             // Always update position - let Leaflet handle everything
+            const oldPos = marker.getLatLng();
+            console.log(`🔄 Updating ${icao}: [${oldPos.lat}, ${oldPos.lng}] -> [${pos[0]}, ${pos[1]}]`);
             marker.setLatLng(pos);
             
             // Update rotation using Leaflet's options if available, otherwise skip rotation

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

@@ -32,6 +32,7 @@ export class MapManager {
         // Store origin for reset functionality
         this.mapOrigin = origin;
         
+        console.log(`🗺️ Map origin: [${origin.latitude}, ${origin.longitude}]`);
         this.map = L.map('map').setView([origin.latitude, origin.longitude], 10);
         
         // Dark tile layer