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/example/.gitignore

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+# Miscellaneous
+*.class
+*.log
+*.pyc
+*.swp
+.DS_Store
+.atom/
+.build/
+.buildlog/
+.history
+.svn/
+.swiftpm/
+migrate_working_dir/
+
+# IntelliJ related
+*.iml
+*.ipr
+*.iws
+.idea/
+
+# The .vscode folder contains launch configuration and tasks you configure in
+# VS Code which you may wish to be included in version control, so this line
+# is commented out by default.
+#.vscode/
+
+# Flutter/Dart/Pub related
+**/doc/api/
+**/ios/Flutter/.last_build_id
+.dart_tool/
+.flutter-plugins-dependencies
+.pub-cache/
+.pub/
+/build/
+/coverage/
+
+# Symbolication related
+app.*.symbols
+
+# Obfuscation related
+app.*.map.json
+
+# Android Studio will place build artifacts here
+/android/app/debug
+/android/app/profile
+/android/app/release

packages/split_button_m3e/example/.metadata

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+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: "d693b4b9dbac2acd4477aea4555ca6dcbea44ba2"
+  channel: "stable"
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+      base_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+    - platform: android
+      create_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+      base_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+    - platform: ios
+      create_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+      base_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+    - platform: linux
+      create_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+      base_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+    - platform: macos
+      create_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+      base_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+    - platform: web
+      create_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+      base_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+    - platform: windows
+      create_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+      base_revision: d693b4b9dbac2acd4477aea4555ca6dcbea44ba2
+
+  # User provided section
+
+  # List of Local paths (relative to this file) that should be
+  # ignored by the migrate tool.
+  #
+  # Files that are not part of the templates will be ignored by default.
+  unmanaged_files:
+    - 'lib/main.dart'
+    - 'ios/Runner.xcodeproj/project.pbxproj'

packages/split_button_m3e/example/README.md

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+# split_button_m3e_example
+
+A new Flutter project.
+
+## Getting Started
+
+This project is a starting point for a Flutter application.
+
+A few resources to get you started if this is your first Flutter project:
+
+- [Lab: Write your first Flutter app](https://docs.flutter.dev/get-started/codelab)
+- [Cookbook: Useful Flutter samples](https://docs.flutter.dev/cookbook)
+
+For help getting started with Flutter development, view the
+[online documentation](https://docs.flutter.dev/), which offers tutorials,
+samples, guidance on mobile development, and a full API reference.

packages/split_button_m3e/example/analysis_options.yaml

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+# This file configures the analyzer, which statically analyzes Dart code to
+# check for errors, warnings, and lints.
+#
+# The issues identified by the analyzer are surfaced in the UI of Dart-enabled
+# IDEs (https://dart.dev/tools#ides-and-editors). The analyzer can also be
+# invoked from the command line by running `flutter analyze`.
+
+# The following line activates a set of recommended lints for Flutter apps,
+# packages, and plugins designed to encourage good coding practices.
+# include: package:flutter_lints/flutter.yaml
+
+linter:
+  # The lint rules applied to this project can be customized in the
+  # section below to disable rules from the `package:flutter_lints/flutter.yaml`
+  # included above or to enable additional rules. A list of all available lints
+  # and their documentation is published at https://dart.dev/lints.
+  #
+  # Instead of disabling a lint rule for the entire project in the
+  # section below, it can also be suppressed for a single line of code
+  # or a specific dart file by using the `// ignore: name_of_lint` and
+  # `// ignore_for_file: name_of_lint` syntax on the line or in the file
+  # producing the lint.
+  rules:
+    # avoid_print: false  # Uncomment to disable the `avoid_print` rule
+    prefer_single_quotes: true  # Uncomment to enable the `prefer_single_quotes` rule
+
+# Additional information about this file can be found at
+# https://dart.dev/guides/language/analysis-options

packages/split_button_m3e/example/lib/main.dart

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+import 'package:flutter/material.dart';
+import 'package:split_button_m3e/split_button_m3e.dart';
+
+void main() => runApp(const DemoApp());
+
+class DemoApp extends StatelessWidget {
+  const DemoApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      debugShowCheckedModeBanner: false,
+      title: 'SplitButtonM3E Demo',
+      theme: ThemeData(
+        useMaterial3: true,
+        colorScheme: ColorScheme.fromSeed(seedColor: Colors.indigo),
+      ),
+      home: const DemoHome(),
+    );
+  }
+}
+
+class DemoHome extends StatelessWidget {
+  const DemoHome({super.key});
+
+  void _snack(BuildContext ctx, String msg) {
+    ScaffoldMessenger.of(ctx).showSnackBar(SnackBar(content: Text(msg)));
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    const sizes = SplitButtonM3ESize.values;
+    const variants = SplitButtonM3EEmphasis.values;
+
+    return Scaffold(
+      appBar: AppBar(title: const Text('SplitButtonM3E Demo')),
+      body: ListView(
+        padding: const EdgeInsets.all(16),
+        children: [
+          const Text('Basic usage',
+              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold)),
+          const SizedBox(height: 8),
+          SplitButtonM3E<String>(
+            label: 'Save',
+            leadingIcon: Icons.save_outlined,
+            onPressed: () => _snack(context, 'Save pressed'),
+            items: const [
+              SplitButtonM3EItem<String>(
+                  value: 'draft', child: 'Save as draft'),
+              SplitButtonM3EItem<String>(value: 'close', child: 'Save & close'),
+            ],
+            onSelected: (v) => _snack(context, 'Selected: $v'),
+          ),
+          const SizedBox(height: 24),
+          const Text('Variants × Sizes (round)',
+              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold)),
+          const SizedBox(height: 8),
+          for (final v in variants) ...[
+            Text(v.toString().split('.').last.toUpperCase(),
+                style: const TextStyle(fontWeight: FontWeight.bold)),
+            const SizedBox(height: 8),
+            Wrap(
+              spacing: 12,
+              runSpacing: 12,
+              children: [
+                for (final s in sizes)
+                  SplitButtonM3E<String>(
+                    label: 'Action',
+                    leadingIcon: Icons.play_arrow,
+                    onPressed: () => _snack(context, 'Primary: $v/$s'),
+                    items: const [
+                      SplitButtonM3EItem<String>(value: 'alt1', child: 'Alt 1'),
+                      SplitButtonM3EItem<String>(value: 'alt2', child: 'Alt 2'),
+                    ],
+                    onSelected: (v) => _snack(context, 'Selected: $v ($s)'),
+                    emphasis: v,
+                    size: s,
+                    shape: SplitButtonM3EShape.round,
+                  ),
+              ],
+            ),
+            const SizedBox(height: 16),
+          ],
+          const SizedBox(height: 24),
+          const Text('Square shape',
+              style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold)),
+          const SizedBox(height: 8),
+          Wrap(
+            spacing: 12,
+            runSpacing: 12,
+            children: [
+              for (final v in variants)
+                SplitButtonM3E<String>(
+                  label: 'Share',
+                  leadingIcon: Icons.share,
+                  onPressed: () => _snack(context, 'Share primary'),
+                  items: const [
+                    SplitButtonM3EItem<String>(
+                        value: 'link', child: 'Copy link'),
+                    SplitButtonM3EItem<String>(value: 'email', child: 'Email'),
+                  ],
+                  onSelected: (v) => _snack(context, 'Selected: $v'),
+                  emphasis: v,
+                  size: SplitButtonM3ESize.md,
+                  shape: SplitButtonM3EShape.square,
+                ),
+            ],
+          ),
+          const SizedBox(height: 32),
+        ],
+      ),
+    );
+  }
+}

packages/split_button_m3e/example/pubspec.yaml

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+name: split_button_m3e_example
+description: Example for split_button_m3e
+publish_to: "none"
+
+environment:
+  sdk: ">=3.2.0 <4.0.0"
+  flutter: ">=3.19.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  split_button_m3e:
+    path: ../
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^4.0.0
+
+flutter:
+  uses-material-design: true