fix(cli): replace unsafe syscalls with x/term.IsTerminal

Gosec G103 flagged the raw ioctl calls. Use golang.org/x/term which
handles platform-specific TTY detection internally, and consolidate
three platform files into one.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: michaelmcnees

go.mod

@@ -137,6 +137,7 @@ require (
 	golang.org/x/net v0.52.0 // indirect
 	golang.org/x/sync v0.20.0 // indirect
 	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/term v0.41.0 // indirect
 	golang.org/x/text v0.35.0 // indirect
 	google.golang.org/api v0.247.0 // indirect
 	google.golang.org/genproto v0.0.0-20250603155806-513f23925822 // indirect

internal/cli/interactive.go

@@ -0,0 +1,12 @@
+package cli
+
+import (
+	"os"
+
+	"golang.org/x/term"
+)
+
+// isInteractive returns true if stdin is a real terminal (not piped or redirected).
+func isInteractive() bool {
+	return term.IsTerminal(int(os.Stdin.Fd()))
+}