refactor(useragent): moved shared CreamPanel and StatePanel into generic widgets

useragent/lib/widgets/cream_frame.dart

@@ -0,0 +1,32 @@
+import 'package:arbiter/theme/palette.dart';
+import 'package:flutter/material.dart';
+
+/// A card-shaped frame with the cream background, rounded corners, and a
+/// subtle border. Use [padding] for interior spacing and [margin] for exterior
+/// spacing.
+class CreamFrame extends StatelessWidget {
+  const CreamFrame({
+    super.key,
+    required this.child,
+    this.padding = EdgeInsets.zero,
+    this.margin,
+  });
+
+  final Widget child;
+  final EdgeInsetsGeometry padding;
+  final EdgeInsetsGeometry? margin;
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      margin: margin,
+      padding: padding,
+      decoration: BoxDecoration(
+        borderRadius: BorderRadius.circular(24),
+        color: Palette.cream,
+        border: Border.all(color: Palette.line),
+      ),
+      child: child,
+    );
+  }
+}