Fix version command and add default action with banner

- Version command now uses mfer.Version constant instead of empty build flags
- Running just 'mfer' shows banner + help
- Unknown commands still return error with exit code 1

internal/cli/entry_test.go

@@ -42,7 +42,7 @@ func TestVersionCommand(t *testing.T) {
 
 	assert.Equal(t, 0, exitCode)
 	stdout := opts.Stdout.(*bytes.Buffer).String()
-	assert.Contains(t, stdout, "1.0.0")
+	assert.Contains(t, stdout, mfer.Version)
 	assert.Contains(t, stdout, "abc123")
 }
 

internal/cli/mfer.go

@@ -50,7 +50,10 @@ func (mfa *CLIApp) printBanner() {
 
 // VersionString returns the version and git revision formatted for display.
 func (mfa *CLIApp) VersionString() string {
-	return fmt.Sprintf("%s (%s)", mfa.version, mfa.gitrev)
+	if mfa.gitrev != "" {
+		return fmt.Sprintf("%s (%s)", mfer.Version, mfa.gitrev)
+	}
+	return mfer.Version
 }
 
 func (mfa *CLIApp) setVerbosity(quiet bool, v int) {
@@ -85,6 +88,13 @@ func (mfa *CLIApp) run(args []string) {
 		EnableBashCompletion: true,
 		Writer:               mfa.Stdout,
 		ErrWriter:            mfa.Stderr,
+		Action: func(c *cli.Context) error {
+			if c.Args().Len() > 0 {
+				return fmt.Errorf("unknown command %q", c.Args().First())
+			}
+			mfa.printBanner()
+			return cli.ShowAppHelp(c)
+		},
 		Flags: []cli.Flag{
 			&cli.BoolFlag{
 				Name:    "verbose",