Refactor button component and add new sections for loading indicators, icons, and navigation; update enums and pubspec description

apps/gallery/lib/sections/icon_button_section.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+import 'package:m3e_collection/m3e_collection.dart';
+
+import 'section_card.dart';
+
+class IconButtonSection extends StatelessWidget {
+  const IconButtonSection({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return SectionCard(
+      title: 'IconButtonM3E',
+      subtitle: 'Generated from enums: variant × size (round shape, default width).',
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          for (final variant in IconButtonM3EVariant.values) ...[
+            Padding(
+              padding: const EdgeInsets.symmetric(vertical: 8),
+              child: Text(variant.name, style: Theme.of(context).textTheme.titleMedium),
+            ),
+            Wrap(
+              spacing: 12,
+              runSpacing: 12,
+              children: [
+                for (final size in IconButtonM3ESize.values)
+                  IconButtonM3E(
+                    icon: const Icon(Icons.favorite),
+                    variant: variant,
+                    size: size,
+                    onPressed: () {},
+                  ),
+              ],
+            ),
+          ],
+        ],
+      ),
+    );
+  }
+}