Add initial configuration, tokens, and widgets for M3E components

- Introduced `.gitignore` and `.metadata` for apps and examples.
- Added Flutter/Dart analysis configurations (`analysis_options.yaml`).
- Implemented foundational tokens and themes for M3E (colors, shapes).
- Created base implementations for `IconButtonM3E` and `SplitButtonM3E`.
- Set up CI workflow (`ci.yaml`) to automate testing and analysis.

packages/split_button_m3e/test/split_button_m3e_test.dart

@@ -0,0 +1,70 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:split_button_m3e/split_button_m3e.dart';
+
+void main() {
+  testWidgets('Semantics: primary and trigger have labels', (tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(useMaterial3: true),
+        home: Material(
+          child: SplitButtonM3E<String>(
+            size: SplitButtonM3ESize.md,
+            shape: SplitButtonM3EShape.round,
+            label: 'Download',
+            leadingIcon: Icons.download_outlined,
+            onPressed: () {},
+            items: const [
+              SplitButtonM3EItem<String>(
+                value: 'zip',
+                child: 'Download as ZIP',
+              ),
+              SplitButtonM3EItem<String>(
+                value: 'pdf',
+                child: 'Download as PDF',
+              ),
+            ],
+            trailingTooltip: 'Open menu',
+            // Optional leading tooltip to also tag the primary segment semantics
+            leadingTooltip: 'Download',
+          ),
+        ),
+      ),
+    );
+
+    // Primary labeled as 'Download'
+    expect(find.bySemanticsLabel('Download'), findsWidgets);
+    // Trigger labeled as 'Open menu'
+    expect(find.bySemanticsLabel('Open menu'), findsOneWidget);
+  });
+
+  testWidgets('Hit targets are >= 48 when size is XS', (tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(useMaterial3: true),
+        home: Material(
+          child: Center(
+            child: SplitButtonM3E<String>(
+              size: SplitButtonM3ESize.xs,
+              shape: SplitButtonM3EShape.round,
+              label: 'Edit',
+              leadingIcon: Icons.edit_outlined,
+              onPressed: () {},
+              items: const [
+                SplitButtonM3EItem<String>(value: 'rename', child: 'Rename'),
+              ],
+              // Use tooltips to ensure we measure the segment containers (not just Text)
+              leadingTooltip: 'Edit',
+              trailingTooltip: 'Open menu',
+            ),
+          ),
+        ),
+      ),
+    );
+
+    final primary = find.bySemanticsLabel('Edit');
+    final trigger = find.bySemanticsLabel('Open menu');
+    expect(tester.getSize(primary).height, greaterThanOrEqualTo(48));
+    expect(tester.getSize(trigger).height, greaterThanOrEqualTo(48));
+  });
+}