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.

apps/gallery/pubspec.yaml

@@ -0,0 +1,16 @@
+name: m3e_gallery
+description: Gallery app for Material 3 Expressive packages.
+publish_to: none
+
+environment:
+  sdk: ">=3.5.0 <4.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  m3e_collection:
+    path: ../../packages/m3e_collection
+  material_color_utilities: ^0.11.0
+
+flutter:
+  uses-material-design: true