feat: 支持服务器主机名排序

- 服务器列表默认按主机名升序并支持表头切换

- 后端按白名单排序并区分分页缓存键

backend/controller/server_sort_test.go

@@ -0,0 +1,27 @@
+package controller
+
+import "testing"
+
+// TestServerOrderClause 验证服务器排序字段仅使用后端白名单表达式。 // Logan.Li
+func TestServerOrderClause(t *testing.T) {
+	tests := []struct {
+		name      string
+		sortField string
+		order     string
+		want      string
+	}{
+		{name: "默认排序", want: "created_at DESC"},
+		{name: "主机名升序", sortField: "hostname", order: "asc", want: "LOWER(hostname) ASC, id ASC"},
+		{name: "主机名降序", sortField: "hostname", order: "desc", want: "LOWER(hostname) DESC, id DESC"},
+		{name: "非法方向回退升序", sortField: "hostname", order: "invalid", want: "LOWER(hostname) ASC, id ASC"},
+		{name: "非法字段回退默认", sortField: "hostname; DROP TABLE sys_servers", order: "asc", want: "created_at DESC"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := serverOrderClause(tt.sortField, tt.order); got != tt.want {
+				t.Fatalf("serverOrderClause(%q, %q) = %q, want %q", tt.sortField, tt.order, got, tt.want)
+			}
+		})
+	}
+}