feat: add Cobra CLI scaffolding with Lipgloss styles

- cmd/gt/main.go: Entry point using Cobra
- internal/cmd/root.go: Root command with description
- internal/cmd/version.go: Version command with build info
- internal/style/style.go: Lipgloss styles for terminal output

Closes gt-u1j.1

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

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

internal/cmd/root.go

@@ -0,0 +1,29 @@
+// Package cmd provides CLI commands for the gt tool.
+package cmd
+
+import (
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "gt",
+	Short: "Gas Town - Multi-agent workspace manager",
+	Long: `Gas Town (gt) manages multi-agent workspaces called rigs.
+
+It coordinates agent spawning, work distribution, and communication
+across distributed teams of AI agents working on shared codebases.`,
+}
+
+// Execute runs the root command
+func Execute() {
+	if err := rootCmd.Execute(); err != nil {
+		os.Exit(1)
+	}
+}
+
+func init() {
+	// Global flags can be added here
+	// rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file")
+}