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>

internal/beast/parser.go

@@ -130,8 +130,13 @@ func (p *Parser) ReadMessage() (*Message, error) {
 	case BeastStatusMsg:
 		// Status messages have variable length, skip for now
 		return p.ReadMessage()
+	case BeastEscape:
+		// Handle double escape sequence (0x1A 0x1A) - skip and continue
+		return p.ReadMessage()
 	default:
-		return nil, fmt.Errorf("unknown message type: 0x%02x", msgType)
+		// Skip unknown message types and continue parsing instead of failing
+		// This makes the parser more resilient to malformed or extended Beast formats
+		return p.ReadMessage()
 	}
 
 	// Read timestamp (6 bytes, 48-bit)