feat: 设置语言精简中英+补全时区；构建节点磁盘显示；浏览器 favicon

- 系统设置：界面语言仅保留 简体中文/English；时区按 亚/欧/美/大洋洲
  分组补全 22 个常用时区
- 构建节点：BuildNode 新增 diskInfo 字段（模型/CRUD/seed），卡片显示
  磁盘用量（未上报显示 —），添加/编辑弹窗可维护
- 新增 favicon.svg（主题渐变火箭图标），index.html 注入 icon 链接

backend/internal/database/database.go

@@ -203,9 +203,9 @@ func seedResources() {
 	if n == 0 {
 		hb := time.Now().Add(-10 * time.Second)
 		DB.Create([]model.BuildNode{
-			{Name: "build-host-01", IP: "10.0.8.11", Labels: `["docker","go","java"]`, MaxConcurrency: 4, Status: "online", CurrentJobs: 1, LastHeartbeat: &hb},
-			{Name: "build-host-02", IP: "10.0.8.12", Labels: `["docker","nodejs"]`, MaxConcurrency: 2, Status: "busy", CurrentJobs: 2, LastHeartbeat: &hb},
-			{Name: "build-host-03", IP: "10.0.8.13", Labels: `["python"]`, MaxConcurrency: 2, Status: "offline", LastHeartbeat: &hb},
+			{Name: "build-host-01", IP: "10.0.8.11", Labels: `["docker","go","java"]`, MaxConcurrency: 4, Status: "online", CurrentJobs: 1, DiskInfo: "78G/200G", LastHeartbeat: &hb},
+			{Name: "build-host-02", IP: "10.0.8.12", Labels: `["docker","nodejs"]`, MaxConcurrency: 2, Status: "busy", CurrentJobs: 2, DiskInfo: "156G/500G", LastHeartbeat: &hb},
+			{Name: "build-host-03", IP: "10.0.8.13", Labels: `["python"]`, MaxConcurrency: 2, Status: "offline", DiskInfo: "45G/100G", LastHeartbeat: &hb},
 		})
 	}
 	DB.Model(&model.WebhookEndpoint{}).Count(&n)

backend/internal/handler/resources.go

@@ -394,7 +394,7 @@ func UpdateBuildNode(c *gin.Context) {
 	}
 	var raw map[string]any
 	_ = c.ShouldBindJSON(&raw)
-	for _, k := range []string{"name", "ip", "labels", "maxConcurrency", "workspacePath", "enabled"} {
+	for _, k := range []string{"name", "ip", "labels", "maxConcurrency", "workspacePath", "diskInfo", "enabled"} {
 		if v, ok := raw[k]; ok {
 			database.DB.Model(&n).Update(k, v)
 		}

backend/internal/model/models.go

@@ -204,6 +204,7 @@ type BuildNode struct {
 	Labels         string     `gorm:"type:text" json:"labels"` // JSON ["docker","go"]
 	MaxConcurrency int        `gorm:"default:2" json:"maxConcurrency"`
 	WorkspacePath  string     `gorm:"default:/data/flowstack-workspace" json:"workspacePath"`
+	DiskInfo       string     `json:"diskInfo"` // 如 "45G/200G"
 	Enabled        bool       `gorm:"default:true" json:"enabled"`
 	Status         string     `gorm:"default:offline" json:"status"` // online|offline|busy
 	CurrentJobs    int        `gorm:"default:0" json:"currentJobs"`