feat(list): show all runtimes without argument and indicate global version

- Make runtime argument optional for list command
- Show all installed versions grouped by runtime when no argument given
- Display "(global)" indicator next to the global default version
- Maintain backward compatibility with `dtvem list <runtime>`

Fixes #54

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: CalvinAllen

src/cmd/list.go

@@ -7,41 +7,96 @@ import (
 )
 
 var listCmd = &cobra.Command{
-	Use:   "list <runtime>",
-	Short: "List installed versions of a runtime",
-	Long: `List all installed versions of a specific runtime.
+	Use:   "list [runtime]",
+	Short: "List installed versions",
+	Long: `List all installed versions of a specific runtime, or all runtimes if none specified.
 
 Examples:
-  dtvem list python
-  dtvem list node`,
-	Args: cobra.ExactArgs(1),
+  dtvem list           # List all installed versions
+  dtvem list python    # List installed Python versions
+  dtvem list node      # List installed Node.js versions`,
+	Args: cobra.MaximumNArgs(1),
 	Run: func(cmd *cobra.Command, args []string) {
-		runtimeName := args[0]
-
-		provider, err := runtime.Get(runtimeName)
-		if err != nil {
-			ui.Error("%v", err)
-			ui.Info("Available runtimes: %v", runtime.List())
-			return
+		if len(args) == 0 {
+			listAllRuntimes()
+		} else {
+			listSingleRuntime(args[0])
 		}
+	},
+}
+
+// listAllRuntimes lists installed versions for all runtimes
+func listAllRuntimes() {
+	providers := runtime.GetAll()
 
-		ui.Header("Installed %s versions:", provider.DisplayName())
+	if len(providers) == 0 {
+		ui.Info("No runtime providers registered")
+		return
+	}
 
+	ui.Header("Installed versions:")
+
+	hasAny := false
+	for _, provider := range providers {
 		versions, err := provider.ListInstalled()
 		if err != nil {
-			ui.Error("%v", err)
-			return
+			ui.Error("  %s: %v", provider.DisplayName(), err)
+			continue
 		}
 
 		if len(versions) == 0 {
-			ui.Info("No versions installed")
-			return
+			continue
 		}
 
+		hasAny = true
+		globalVersion, _ := provider.GlobalVersion()
+
+		ui.Printf("  %s:\n", ui.Highlight(provider.DisplayName()))
 		for _, v := range versions {
+			if v.String() == globalVersion {
+				ui.Printf("    %s (global)\n", ui.HighlightVersion(v.String()))
+			} else {
+				ui.Printf("    %s\n", ui.HighlightVersion(v.String()))
+			}
+		}
+	}
+
+	if !hasAny {
+		ui.Info("No versions installed")
+	}
+}
+
+// listSingleRuntime lists installed versions for a specific runtime
+func listSingleRuntime(runtimeName string) {
+	provider, err := runtime.Get(runtimeName)
+	if err != nil {
+		ui.Error("%v", err)
+		ui.Info("Available runtimes: %v", runtime.List())
+		return
+	}
+
+	ui.Header("Installed %s versions:", provider.DisplayName())
+
+	versions, err := provider.ListInstalled()
+	if err != nil {
+		ui.Error("%v", err)
+		return
+	}
+
+	if len(versions) == 0 {
+		ui.Info("No versions installed")
+		return
+	}
+
+	globalVersion, _ := provider.GlobalVersion()
+
+	for _, v := range versions {
+		if v.String() == globalVersion {
+			ui.Printf("  %s (global)\n", ui.HighlightVersion(v.String()))
+		} else {
 			ui.Printf("  %s\n", ui.HighlightVersion(v.String()))
 		}
-	},
+	}
 }
 
 func init() {