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>

cmd/gt/main.go

@@ -1,15 +1,8 @@
+// gt is the Gas Town CLI for managing multi-agent workspaces.
 package main
 
-import (
-	"fmt"
-	"os"
-)
+import "github.com/steveyegge/gastown/internal/cmd"
 
 func main() {
-	fmt.Println("gt - Gas Town CLI")
-	fmt.Println("Version: 0.0.1 (development)")
-	if len(os.Args) > 1 {
-		fmt.Printf("Command: %s\n", os.Args[1])
-		fmt.Println("Not yet implemented. See gastown-py for current functionality.")
-	}
+	cmd.Execute()
 }