feat: LokiDeploy 初始提交 - 轻量级 K8s Loki 部署平台

Go(Gin) + React(Vite + shadcn/ui + Tailwind) 前后端分离，全中文 UI

- 集群管理：Kubeconfig / Token 双接入，kubectl + helm 部署
- 主机管理：SSH 密钥 / 密码双认证，CPU/内存/磁盘使用率监控，SSH 错误中文友好提示
- 存储配置、部署管理、系统设置
- Docker 镜像内置 kubectl + helm，开箱即用
- run.sh 一键启停（start/stop/restart/status）

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

backend/config/config.go

@@ -0,0 +1,42 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"sync"
+)
+
+var (
+	instance *Config
+	once     sync.Once
+)
+
+type Config struct {
+	ServerPort   string
+	DatabasePath string
+	JWTSecret    string
+	DataDir      string
+	KubeDir      string
+}
+
+func GetConfig() *Config {
+	once.Do(func() {
+		dataDir := getEnv("DATA_DIR", "./data")
+		instance = &Config{
+			ServerPort:   getEnv("SERVER_PORT", "8080"),
+			DatabasePath: filepath.Join(dataDir, "lokideploy.json"),
+			JWTSecret:    getEnv("JWT_SECRET", "lokideploy-secret-key-change-in-production"),
+			DataDir:      dataDir,
+			KubeDir:      filepath.Join(dataDir, "kubeconfigs"),
+		}
+		_ = os.MkdirAll(instance.KubeDir, 0755)
+	})
+	return instance
+}
+
+func getEnv(key, defaultVal string) string {
+	if val := os.Getenv(key); val != "" {
+		return val
+	}
+	return defaultVal
+}