Add checkbox folder browsers

internal/platform/browser_test.go

@@ -0,0 +1,11 @@
+package platform
+
+import "testing"
+
+func TestValidateBrowsePathRejectsUnsafePaths(t *testing.T) {
+	for _, path := range []string{"", "/", "/etc", "/mnt/user/../../etc", "relative"} {
+		if _, err := validateBrowsePath(path); err == nil {
+			t.Fatalf("unsafe browse path accepted: %q", path)
+		}
+	}
+}