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/style/style.go

@@ -0,0 +1,65 @@
+// Package style provides consistent terminal styling using Lipgloss.
+package style
+
+import "github.com/charmbracelet/lipgloss"
+
+var (
+	// Success style for positive outcomes
+	Success = lipgloss.NewStyle().
+		Foreground(lipgloss.Color("10")). // Green
+		Bold(true)
+
+	// Warning style for cautionary messages
+	Warning = lipgloss.NewStyle().
+		Foreground(lipgloss.Color("11")). // Yellow
+		Bold(true)
+
+	// Error style for failures
+	Error = lipgloss.NewStyle().
+		Foreground(lipgloss.Color("9")). // Red
+		Bold(true)
+
+	// Info style for informational messages
+	Info = lipgloss.NewStyle().
+		Foreground(lipgloss.Color("12")) // Blue
+
+	// Dim style for secondary information
+	Dim = lipgloss.NewStyle().
+		Foreground(lipgloss.Color("8")) // Gray
+
+	// Bold style for emphasis
+	Bold = lipgloss.NewStyle().
+		Bold(true)
+
+	// SuccessPrefix is the checkmark prefix for success messages
+	SuccessPrefix = Success.Render("✓")
+
+	// WarningPrefix is the warning prefix
+	WarningPrefix = Warning.Render("⚠")
+
+	// ErrorPrefix is the error prefix
+	ErrorPrefix = Error.Render("✗")
+
+	// ArrowPrefix for action indicators
+	ArrowPrefix = Info.Render("→")
+)
+
+// RenderSuccess formats a success message
+func RenderSuccess(msg string) string {
+	return SuccessPrefix + " " + msg
+}
+
+// RenderWarning formats a warning message
+func RenderWarning(msg string) string {
+	return WarningPrefix + " " + msg
+}
+
+// RenderError formats an error message
+func RenderError(msg string) string {
+	return ErrorPrefix + " " + msg
+}
+
+// RenderInfo formats an info message with arrow
+func RenderInfo(msg string) string {
+	return ArrowPrefix + " " + msg
+}