add initial project structure with configuration, models, and API key authentication

internal/config/config.go

@@ -0,0 +1,34 @@
+package config
+
+import (
+	"os"
+	"strings"
+)
+
+type Config struct {
+	Port    string
+	DSN     string
+	APIKeys []string
+}
+
+func Load() *Config {
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "8080"
+	}
+
+	raw := os.Getenv("API_KEYS")
+	var keys []string
+	for _, k := range strings.Split(raw, ",") {
+		k = strings.TrimSpace(k)
+		if k != "" {
+			keys = append(keys, k)
+		}
+	}
+
+	return &Config{
+		Port:    port,
+		DSN:     os.Getenv("DB_DSN"),
+		APIKeys: keys,
+	}
+}