Fix aircraft markers not updating positions in real-time

Root cause: The merger was blocking position updates from the same source
after the first position was established, designed for multi-source scenarios
but preventing single-source position updates.

Changes:
- Refactor JavaScript into modular architecture (WebSocketManager, AircraftManager, MapManager, UIManager)
- Add CPR coordinate validation to prevent invalid latitude/longitude values
- Fix merger to allow position updates from same source for moving aircraft
- Add comprehensive coordinate bounds checking in CPR decoder
- Update HTML to use new modular JavaScript with cache busting
- Add WebSocket debug logging to track data flow

Technical details:
- CPR decoder now validates coordinates within ±90° latitude, ±180° longitude
- Merger allows updates when currentBest == sourceID (same source continuous updates)
- JavaScript modules provide better separation of concerns and debugging
- WebSocket properly transmits updated aircraft coordinates to frontend

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

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

assets/static/index.html

@@ -222,6 +222,6 @@
     <script src="https://unpkg.com/leaflet@1.9.4/dist/leaflet.js"></script>
     
     <!-- Custom JS -->
-    <script type="module" src="/static/js/app.js"></script>
+    <script type="module" src="/static/js/app-new.js?v=3"></script>
 </body>
 </html>