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/js/modules/websocket.js

@@ -0,0 +1,70 @@
+// WebSocket communication module
+export class WebSocketManager {
+    constructor(onMessage, onStatusChange) {
+        this.websocket = null;
+        this.onMessage = onMessage;
+        this.onStatusChange = onStatusChange;
+    }
+
+    async connect() {
+        const protocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
+        const wsUrl = `${protocol}//${window.location.host}/ws`;
+        
+        try {
+            this.websocket = new WebSocket(wsUrl);
+            
+            this.websocket.onopen = () => {
+                console.log('WebSocket connected');
+                this.onStatusChange('connected');
+            };
+            
+            this.websocket.onclose = () => {
+                console.log('WebSocket disconnected');
+                this.onStatusChange('disconnected');
+                // Reconnect after 5 seconds
+                setTimeout(() => this.connect(), 5000);
+            };
+            
+            this.websocket.onerror = (error) => {
+                console.error('WebSocket error:', error);
+                this.onStatusChange('disconnected');
+            };
+            
+            this.websocket.onmessage = (event) => {
+                try {
+                    const message = JSON.parse(event.data);
+                    
+                    // Debug: Log WebSocket messages to see what we're receiving
+                    if (message.data && message.data.aircraft) {
+                        const aircraftCount = Object.keys(message.data.aircraft).length;
+                        console.log(`📡 WebSocket: ${message.type} with ${aircraftCount} aircraft`);
+                        
+                        // Log first few aircraft with coordinates
+                        let count = 0;
+                        for (const [icao, aircraft] of Object.entries(message.data.aircraft)) {
+                            if (count < 3 && aircraft.Latitude && aircraft.Longitude) {
+                                console.log(`📡 ${icao}: lat=${aircraft.Latitude}, lon=${aircraft.Longitude}`);
+                            }
+                            count++;
+                        }
+                    }
+                    
+                    this.onMessage(message);
+                } catch (error) {
+                    console.error('Failed to parse WebSocket message:', error);
+                }
+            };
+            
+        } catch (error) {
+            console.error('WebSocket connection failed:', error);
+            this.onStatusChange('disconnected');
+        }
+    }
+
+    disconnect() {
+        if (this.websocket) {
+            this.websocket.close();
+            this.websocket = null;
+        }
+    }
+}