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

apps/gallery/lib/sections/slider_section.dart

@@ -0,0 +1,73 @@
+import 'package:flutter/material.dart';
+import 'package:m3e_collection/m3e_collection.dart';
+
+import 'section_card.dart';
+
+class SliderSection extends StatefulWidget {
+  const SliderSection({super.key});
+
+  @override
+  State<SliderSection> createState() => _SliderSectionState();
+}
+
+class _SliderSectionState extends State<SliderSection> {
+  double _value = 40;
+  RangeValues _range = const RangeValues(25, 75);
+
+  @override
+  Widget build(BuildContext context) {
+    return SectionCard(
+      title: 'SliderM3E',
+      subtitle: 'Generated from enums: size × emphasis (round shape).',
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          for (final size in SliderM3ESize.values) ...[
+            Padding(
+              padding: const EdgeInsets.symmetric(vertical: 8),
+              child: Text('size: ${size.name}', style: Theme.of(context).textTheme.titleMedium),
+            ),
+            Wrap(
+              runSpacing: 12,
+              children: [
+                for (final emp in SliderM3EEmphasis.values)
+                  Padding(
+                    padding: const EdgeInsets.only(bottom: 8),
+                    child: Column(
+                      crossAxisAlignment: CrossAxisAlignment.start,
+                      children: [
+                        Text('emphasis: ${emp.name}', style: Theme.of(context).textTheme.labelLarge),
+                        SliderM3E(
+                          value: _value,
+                          onChanged: (v) => setState(() => _value = v),
+                          min: 0,
+                          max: 100,
+                          label: _value.toStringAsFixed(0),
+                          size: size,
+                          emphasis: emp,
+                          startIcon: const Icon(Icons.volume_mute),
+                          endIcon: const Icon(Icons.volume_up),
+                        ),
+                        RangeSliderM3E(
+                          values: _range,
+                          onChanged: (v) => setState(() => _range = v),
+                          min: 0,
+                          max: 100,
+                          size: size,
+                          emphasis: emp,
+                          labels: RangeLabels(
+                            _range.start.toStringAsFixed(0),
+                            _range.end.toStringAsFixed(0),
+                          ),
+                        ),
+                      ],
+                    ),
+                  ),
+              ],
+            ),
+          ],
+        ],
+      ),
+    );
+  }
+}