Use config from .env and update api

src/config/config.go

@@ -0,0 +1,66 @@
+package config
+
+import (
+	"os"
+	"strconv"
+	"time"
+)
+
+type Config struct {
+	Server struct {
+		Port string
+		Mode string // gin.Mode: debug, release, test
+	}
+	JWT struct {
+		Secret string
+	}
+	Sync struct {
+		Interval time.Duration
+	}
+	Admin struct {
+		Email    string
+		Password string
+	}
+	SheetsDirectory string
+}
+
+var AppConfig *Config
+
+func Load() {
+	cfg := &Config{}
+
+	// Server configuration
+	cfg.Server.Port = getEnv("SERVER_PORT", ":8080")
+	cfg.Server.Mode = getEnv("GIN_MODE", "debug")
+
+	// JWT configuration
+	cfg.JWT.Secret = getEnv("JWT_SECRET", "sheetless-default-jwt-secret-please-change")
+
+	// Sync configuration
+	syncMinutes := getEnvInt("SYNC_INTERVAL_MINUTES", 1)
+	cfg.Sync.Interval = time.Duration(syncMinutes) * time.Minute
+
+	// Admin configuration
+	cfg.Admin.Email = getEnv("ADMIN_EMAIL", "admin@admin.com")
+	cfg.Admin.Password = getEnv("ADMIN_PASSWORD", "sheetless")
+
+	cfg.SheetsDirectory = getEnv("SHEETS_DIRECTORY", "./sheets_directory")
+
+	AppConfig = cfg
+}
+
+func getEnv(key, defaultValue string) string {
+	if value := os.Getenv(key); value != "" {
+		return value
+	}
+	return defaultValue
+}
+
+func getEnvInt(key string, defaultValue int) int {
+	if value := os.Getenv(key); value != "" {
+		if intValue, err := strconv.Atoi(value); err == nil {
+			return intValue
+		}
+	}
+	return defaultValue
+}