Initial implementation of SkyView - ADS-B aircraft tracker

- Go application with embedded static files for dump1090 frontend
- TCP client for SBS-1/BaseStation format (port 30003)
- Real-time WebSocket updates with aircraft tracking
- Modern web frontend with Leaflet maps and mobile-responsive design
- Aircraft table with filtering/sorting and statistics dashboard
- Origin configuration for receiver location and distance calculations
- Automatic config.json loading from current directory
- Foreground execution by default with optional -daemon flag

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

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

internal/config/config.go

@@ -0,0 +1,118 @@
+package config
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type Config struct {
+	Server   ServerConfig   `json:"server"`
+	Dump1090 Dump1090Config `json:"dump1090"`
+	Origin   OriginConfig   `json:"origin"`
+}
+
+type ServerConfig struct {
+	Address string `json:"address"`
+	Port    int    `json:"port"`
+}
+
+type Dump1090Config struct {
+	Host     string `json:"host"`
+	DataPort int    `json:"data_port"`
+}
+
+type OriginConfig struct {
+	Latitude  float64 `json:"latitude"`
+	Longitude float64 `json:"longitude"`
+	Name      string  `json:"name"`
+}
+
+func Load() (*Config, error) {
+	cfg := &Config{
+		Server: ServerConfig{
+			Address: ":8080",
+			Port:    8080,
+		},
+		Dump1090: Dump1090Config{
+			Host:     "localhost",
+			DataPort: 30003,
+		},
+		Origin: OriginConfig{
+			Latitude:  37.7749,
+			Longitude: -122.4194,
+			Name:      "Default Location",
+		},
+	}
+
+	configFile := os.Getenv("SKYVIEW_CONFIG")
+	if configFile == "" {
+		// Check for config files in common locations
+		candidates := []string{"config.json", "./config.json", "skyview.json"}
+		for _, candidate := range candidates {
+			if _, err := os.Stat(candidate); err == nil {
+				configFile = candidate
+				break
+			}
+		}
+	}
+
+	if configFile != "" {
+		if err := loadFromFile(cfg, configFile); err != nil {
+			return nil, fmt.Errorf("failed to load config file %s: %w", configFile, err)
+		}
+	}
+
+	loadFromEnv(cfg)
+
+	return cfg, nil
+}
+
+func loadFromFile(cfg *Config, filename string) error {
+	data, err := os.ReadFile(filename)
+	if err != nil {
+		return err
+	}
+
+	return json.Unmarshal(data, cfg)
+}
+
+func loadFromEnv(cfg *Config) {
+	if addr := os.Getenv("SKYVIEW_ADDRESS"); addr != "" {
+		cfg.Server.Address = addr
+	}
+
+	if portStr := os.Getenv("SKYVIEW_PORT"); portStr != "" {
+		if port, err := strconv.Atoi(portStr); err == nil {
+			cfg.Server.Port = port
+			cfg.Server.Address = fmt.Sprintf(":%d", port)
+		}
+	}
+
+	if host := os.Getenv("DUMP1090_HOST"); host != "" {
+		cfg.Dump1090.Host = host
+	}
+
+	if dataPortStr := os.Getenv("DUMP1090_DATA_PORT"); dataPortStr != "" {
+		if port, err := strconv.Atoi(dataPortStr); err == nil {
+			cfg.Dump1090.DataPort = port
+		}
+	}
+
+	if latStr := os.Getenv("ORIGIN_LATITUDE"); latStr != "" {
+		if lat, err := strconv.ParseFloat(latStr, 64); err == nil {
+			cfg.Origin.Latitude = lat
+		}
+	}
+
+	if lonStr := os.Getenv("ORIGIN_LONGITUDE"); lonStr != "" {
+		if lon, err := strconv.ParseFloat(lonStr, 64); err == nil {
+			cfg.Origin.Longitude = lon
+		}
+	}
+
+	if name := os.Getenv("ORIGIN_NAME"); name != "" {
+		cfg.Origin.Name = name
+	}
+}