test: disable parallel execution to fix data races

Removes t.Parallel() from TestRadioMenu_Unit, TestShowVersion_Unit,
and TestPrecheck_Unit. These tests mutate globals, redirect os.Stdout,
or call external dependencies, causing races when run concurrently
with other tests under -race.

radiomenu_test.go

@@ -78,7 +78,10 @@ func TestQuit_Unit(t *testing.T) {
 }
 
 func TestRadioMenu_Unit(t *testing.T) {
-	t.Parallel()
+	// Do not mark Parallel: RadioMenu does fmt.Println and constructs a wmenu.Menu.
+	// When this runs concurrently (via t.Parallel on the parent) with
+	// TestShowVersion_Unit (which mutates globals and does os.Stdout swapping),
+	// the race detector flags concurrent fmt + wmenu activity against global writes.
 	t.Log("✓ Fast RadioMenu unit test")
 
 	tests := []struct {

stations_test.go

@@ -15,7 +15,10 @@ import (
 )
 
 func TestShowVersion_Unit(t *testing.T) {
-	t.Parallel()
+	// Do not mark Parallel: this test mutates the package-level "version" shim
+	// (and internal/version vars) and redirects os.Stdout. Running it concurrently
+	// with other legacy tests (esp. those calling RadioMenu which does fmt + wmenu)
+	// produces data races under -race.
 	t.Log("✓ Fast showVersion unit test")
 
 	tests := []struct {
@@ -81,7 +84,9 @@ func TestShowVersion_Unit(t *testing.T) {
 }
 
 func TestPrecheck_Unit(t *testing.T) {
-	t.Parallel()
+	// Do not mark Parallel: precheck reads config + calls external IsInstalled,
+	// and in some paths can have side effects. Keep it serialized with other
+	// main-package legacy tests to avoid races on shared state under -race.
 	t.Log("✓ Fast precheck unit test")
 
 	p := "mpv"