Add VRS JSON format support for readsb integration

Added comprehensive support for VRS (Virtual Radar Server) JSON format
as a simpler alternative to Beast binary protocol, enabling integration
with readsb --net-vrs-port output.

## Key Features:
- **VRS JSON Parser**: Stream parsing of newline-delimited JSON aircraft data
- **VRS Client**: TCP client with automatic reconnection and error recovery
- **Mixed Format Support**: Use Beast and VRS sources simultaneously
- **Enhanced Aircraft Data**: Added VRS-specific fields (registration, type, operator)
- **Position Source Tracking**: Identifies ADS-B, MLAT, TIS-B, and satellite positions

## Implementation:
- `internal/vrs/parser.go`: VRS JSON message parsing and validation
- `internal/client/vrs.go`: VRS TCP client implementation
- Enhanced `MultiSourceClient` to support both Beast and VRS formats
- Extended `Aircraft` struct with validity flags and additional metadata
- Updated configuration to include `format` field ("beast" or "vrs")

## Testing:
- Successfully tested against svovel:33005 VRS JSON stream
- Verified aircraft data parsing and position tracking
- Confirmed mixed-format operation with existing Beast clients

## Documentation:
- Updated README.md with VRS format configuration examples
- Enhanced ARCHITECTURE.md with VRS parser documentation
- Added data format comparison and configuration guide

This enables simpler integration with modern readsb installations while
maintaining full backward compatibility with existing Beast deployments.

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

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

cmd/vrs-test/main.go

@@ -0,0 +1,133 @@
+// Package main implements a simple VRS JSON parser test utility.
+//
+// This utility connects to a VRS JSON source and displays the parsed
+// aircraft data for testing and debugging purposes.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"skyview/internal/vrs"
+)
+
+func main() {
+	host := flag.String("host", "svovel", "VRS host to connect to")
+	port := flag.Int("port", 33005, "VRS port to connect to")
+	flag.Parse()
+
+	fmt.Printf("Connecting to VRS JSON source at %s:%d...\n", *host, *port)
+
+	// Connect to VRS source
+	addr := fmt.Sprintf("%s:%d", *host, *port)
+	conn, err := net.DialTimeout("tcp", addr, 30*time.Second)
+	if err != nil {
+		log.Fatalf("Failed to connect to %s: %v", addr, err)
+	}
+	defer conn.Close()
+
+	fmt.Printf("Connected to %s\n", addr)
+
+	// Create VRS parser
+	parser := vrs.NewParser(conn, "test")
+
+	// Set up channels for messages and errors
+	msgChan := make(chan *vrs.VRSMessage, 100)
+	errChan := make(chan error, 10)
+
+	// Set up signal handling
+	ctx, cancel := context.WithCancel(context.Background())
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
+
+	// Start parsing in background
+	go parser.ParseStream(msgChan, errChan)
+
+	// Statistics tracking
+	messageCount := 0
+	aircraftCount := 0
+	startTime := time.Now()
+
+	fmt.Println("Receiving VRS JSON data... (Press Ctrl+C to stop)")
+	fmt.Println("----------------------------------------")
+
+	for {
+		select {
+		case <-ctx.Done():
+			fmt.Println("\nShutting down...")
+			return
+
+		case <-sigChan:
+			fmt.Println("\nReceived interrupt signal")
+			cancel()
+
+		case err := <-errChan:
+			log.Printf("Parser error: %v", err)
+			cancel()
+
+		case msg := <-msgChan:
+			if msg == nil {
+				cancel()
+				continue
+			}
+
+			messageCount++
+			aircraftCount += len(msg.AcList)
+
+			fmt.Printf("Message %d: %d aircraft\n", messageCount, len(msg.AcList))
+
+			// Display first few aircraft for debugging
+			for i, ac := range msg.AcList {
+				if i >= 3 { // Only show first 3 aircraft per message
+					fmt.Printf("  ... and %d more aircraft\n", len(msg.AcList)-i)
+					break
+				}
+
+				icao, _ := ac.GetICAO24()
+				fmt.Printf("  ICAO: %06X", icao)
+
+				if ac.Call != "" {
+					fmt.Printf("  Call: %-8s", ac.Call)
+				}
+
+				if ac.HasPosition() {
+					fmt.Printf("  Pos: %7.3f°, %8.3f°", ac.Lat, ac.Long)
+				}
+
+				if ac.HasAltitude() {
+					fmt.Printf("  Alt: %5d ft", ac.GetAltitude())
+				}
+
+				if ac.Spd > 0 {
+					fmt.Printf("  Spd: %3.0f kt", ac.Spd)
+				}
+
+				if ac.Trak > 0 {
+					fmt.Printf("  Hdg: %3.0f°", ac.Trak)
+				}
+
+				if ac.Gnd {
+					fmt.Printf("  [GND]")
+				}
+
+				fmt.Printf("  Src: %s\n", ac.GetPositionSource())
+			}
+
+			// Show statistics every 10 messages
+			if messageCount%10 == 0 {
+				elapsed := time.Since(startTime)
+				fmt.Printf("Stats: %d messages, %d total aircraft, %.1fs elapsed\n",
+					messageCount, aircraftCount, elapsed.Seconds())
+			}
+
+			fmt.Println("----------------------------------------")
+		}
+	}
+}