feat(version): 第18条 显示版本与内部版本解耦（V/A 双系）

- config 新增 displayVersion 注入变量（默认 1.0.0）：GetDisplayVersion/
  GetMasterDisplayVersion(V)/GetAgentDisplayVersion(A)，以后升版只改注入值
- ParseDisplayVersion/CompareDisplayVersion：三段数值比较，个位进位规则
  (1.0.9<1.1.0) 天然成立；不可解析（dev 标签/3.7.0-agent.1）返回 ok=false
- 显示位切换：dist 注入 X_UI_CUR_VER、-v、TG 报告 → V 系；
  agent 遥测 agentVersion → A 系；节点行 A 系原样显示、老 agent 沿用
  "agent " 前缀兼容
- 内部流不动：GetBaseVersion/GetPanelVersion 及其比较/订阅/远端状态
  消费方保持原样，传统节点更新判定与徽标行为不变

internal/config/config_test.go

@@ -53,6 +53,78 @@ func TestGetBaseVersionBuildVersionOverride(t *testing.T) {
 	}
 }
 
+func TestDisplayVersionDefaultsAndOverride(t *testing.T) {
+	orig := displayVersion
+	t.Cleanup(func() { displayVersion = orig })
+
+	displayVersion = ""
+	if got := GetDisplayVersion(); got != "1.0.0" {
+		t.Fatalf("default display version = %q, want 1.0.0", got)
+	}
+	if got := GetMasterDisplayVersion(); got != "V1.0.0" {
+		t.Fatalf("default master display version = %q, want V1.0.0", got)
+	}
+	if got := GetAgentDisplayVersion(); got != "A1.0.0" {
+		t.Fatalf("default agent display version = %q, want A1.0.0", got)
+	}
+
+	displayVersion = "1.0.1"
+	if got := GetMasterDisplayVersion(); got != "V1.0.1" {
+		t.Fatalf("injected master display version = %q, want V1.0.1", got)
+	}
+	if got := GetAgentDisplayVersion(); got != "A1.0.1" {
+		t.Fatalf("injected agent display version = %q, want A1.0.1", got)
+	}
+}
+
+func TestParseDisplayVersion(t *testing.T) {
+	valid := map[string][3]int{
+		"1.0.0":   {1, 0, 0},
+		"V1.0.0":  {1, 0, 0},
+		"A1.0.9":  {1, 0, 9},
+		"v2.0.0":  {2, 0, 0},
+		" 1.2.3 ": {1, 2, 3},
+	}
+	for in, want := range valid {
+		got, ok := ParseDisplayVersion(in)
+		if !ok || got != want {
+			t.Fatalf("ParseDisplayVersion(%q) = %v, %v; want %v, true", in, got, ok, want)
+		}
+	}
+	invalid := []string{"", "3.7.0-agent.1", "dev+1a2b3c4d", "1.0", "1.0.0.1", "1.x.0", "V", "1..0"}
+	for _, in := range invalid {
+		if _, ok := ParseDisplayVersion(in); ok {
+			t.Fatalf("ParseDisplayVersion(%q) ok=true, want false", in)
+		}
+	}
+}
+
+func TestCompareDisplayVersion(t *testing.T) {
+	cases := []struct {
+		a, b string
+		want int
+	}{
+		{"1.0.0", "1.0.0", 0},
+		{"V1.0.0", "A1.0.0", 0},  // prefix letters are flavour, not value
+		{"1.0.9", "1.1.0", -1},   // single-digit carry step
+		{"1.1.0", "1.0.9", 1},    // carry compares numerically, not lexically
+		{"1.9.9", "2.0.0", -1},   // full carry
+		{"A1.0.1", "A1.0.0", 1},  // agent series
+		{"V1.0.1", "1.0.0", 1},   // release tag vs current
+		{"2.0.0", "1.9.9", 1},
+		{"1.0.0", "1.0.1", -1},
+	}
+	for _, tc := range cases {
+		got, ok := CompareDisplayVersion(tc.a, tc.b)
+		if !ok || got != tc.want {
+			t.Fatalf("CompareDisplayVersion(%q, %q) = %d, %v; want %d, true", tc.a, tc.b, got, ok, tc.want)
+		}
+	}
+	if _, ok := CompareDisplayVersion("3.7.0-agent.1", "1.0.0"); ok {
+		t.Fatal("unparseable side must report ok=false")
+	}
+}
+
 func TestGetPortOverride(t *testing.T) {
 	tests := []struct {
 		name       string