feat: 优化非 Docker 命令的易用性，修复带 digest 镜像无法按名称查找

- docker save/rmi：镜像名不再拼接 digest（{{.Digest}} 对多数镜像输出
  sha256:…，导致 alpine:3.20 被存成 alpine:3.20@sha256:… 而查不到），
  digest 单独保存；同时修正自定义 --format 输出中 IMAGE ID 表头未被过滤
- diagnose：目标不存在时给出相似名称候选，无相似时列出当前存在的对象
- net.pids：无进程占用时向 stderr 提示且 stdout 保持为空，新增 --pid-file
- net.ports：默认输出跨平台一致的端口表格，--raw 保留原生命令输出
- disk.usage：路径可省略（默认当前目录），新增 --depth N 控制层级

internal/diagnose/service_test.go

@@ -138,3 +138,79 @@ func TestResolveNamespaceSkipsDocker(t *testing.T) {
 		t.Errorf("namespace missing from output:\n%s", out.String())
 	}
 }
+
+func TestResolveNotFoundSuggestsSimilarContainers(t *testing.T) {
+	r := &fakeRunner{
+		available: map[string]bool{"docker": true, "kubectl": true},
+		respond: func(name string, args []string) (CommandResult, error) {
+			joined := strings.Join(args, " ")
+			switch {
+			case len(args) > 0 && args[0] == "inspect":
+				return CommandResult{Stdout: []byte("[]")}, nil
+			case strings.HasPrefix(joined, "ps -a"):
+				return CommandResult{Stdout: []byte("web-1\nweb-2\ndb\nnginx-web\n")}, nil
+			case strings.HasPrefix(joined, "config view"):
+				return CommandResult{}, nil
+			case strings.HasPrefix(joined, "get pod"):
+				return CommandResult{Stderr: []byte("not found")}, fmt.Errorf("exit status 1")
+			}
+			return CommandResult{}, nil
+		},
+	}
+
+	s, _, _ := newTestService(r)
+	err := s.Run(context.Background(), []string{"web"})
+	if err == nil || !strings.Contains(err.Error(), "未找到目标") {
+		t.Fatalf("err = %v, want not-found error", err)
+	}
+	msg := err.Error()
+	for _, want := range []string{"你可能要找的是", "web-1", "web-2"} {
+		if !strings.Contains(msg, want) {
+			t.Errorf("error missing %q:\n%s", want, msg)
+		}
+	}
+}
+
+func TestResolveNotFoundWithoutCandidatesKeepsOriginalText(t *testing.T) {
+	r := &fakeRunner{
+		available: map[string]bool{"docker": true},
+		respond: func(name string, args []string) (CommandResult, error) {
+			switch {
+			case len(args) > 0 && args[0] == "inspect":
+				return CommandResult{Stdout: []byte("[]")}, nil
+			case strings.HasPrefix(strings.Join(args, " "), "ps -a"):
+				return CommandResult{Stdout: []byte("alpha\nbeta\n")}, nil
+			}
+			return CommandResult{}, nil
+		},
+	}
+
+	s, _, _ := newTestService(r)
+	err := s.Run(context.Background(), []string{"ghost"})
+	if err == nil || !strings.Contains(err.Error(), "未找到目标") {
+		t.Fatalf("err = %v, want not-found error", err)
+	}
+	if strings.Contains(err.Error(), "你可能要找的是") {
+		t.Errorf("unexpected candidate hint:\n%s", err.Error())
+	}
+	// Nothing is similar, so the existing objects are listed instead.
+	for _, want := range []string{"当前存在的对象", "alpha", "beta"} {
+		if !strings.Contains(err.Error(), want) {
+			t.Errorf("error missing %q:\n%s", want, err.Error())
+		}
+	}
+}
+
+func TestMatchNamesRanking(t *testing.T) {
+	names := []string{"nginx-web", "web-1", "WEB-2", "api", "myweb"}
+	got := matchNames(names, "web")
+	want := []string{"web-1", "WEB-2", "nginx-web", "myweb"}
+	if strings.Join(got, ",") != strings.Join(want, ",") {
+		t.Fatalf("matchNames() = %v, want %v (prefix hits first, case-insensitive)", got, want)
+	}
+
+	many := []string{"web-1", "web-2", "web-3", "web-4", "web-5", "web-6", "web-7"}
+	if got := matchNames(many, "web"); len(got) != 5 {
+		t.Fatalf("matchNames returned %d names, want the 5 closest", len(got))
+	}
+}