fix: Remove t.Parallel from tests that modify os.Stderr

These tests modify os.Stderr to capture output, which is a global
variable that cannot be safely accessed in parallel. Add nolint
comments explaining why t.Parallel cannot be used.

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

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

Author: cv

internal/cli/root_test.go

@@ -141,8 +141,10 @@ func TestExecute_WithRealSignal(t *testing.T) {
 	}
 }
 
+// TestCheckSkillVersionMismatch_SkipsSkillCommands tests that skill commands are skipped.
+//
+//nolint:paralleltest // This test modifies os.Stderr which is a global variable.
 func TestCheckSkillVersionMismatch_SkipsSkillCommands(t *testing.T) {
-	t.Parallel()
 	// Create a skill command with context containing config
 	skillCmd := &cobra.Command{Use: "skill"}
 	cfg := testCLIConfig()
@@ -166,8 +168,10 @@ func TestCheckSkillVersionMismatch_SkipsSkillCommands(t *testing.T) {
 	assert.Empty(t, errBuf.String())
 }
 
+// TestCheckSkillVersionMismatch_SkipsSkillSubcommands tests that skill subcommands are skipped.
+//
+//nolint:paralleltest // This test modifies os.Stderr which is a global variable.
 func TestCheckSkillVersionMismatch_SkipsSkillSubcommands(t *testing.T) {
-	t.Parallel()
 	// Create a skill subcommand (e.g., skill install)
 	skillCmd := &cobra.Command{Use: "skill"}
 	installCmd := &cobra.Command{Use: "install"}