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/button_m3e/README.md

@@ -0,0 +1,70 @@
+# button_m3e
+
+Material 3 **Expressive** Buttons for Flutter, built on top of Flutter's buttons but styled via **M3E** tokens.
+
+Variants: **filled**, **tonal**, **outlined**, **text**, **elevated**  
+Sizes: **small**, **medium**, **large**  
+Shape families: **round**, **square**  
+Density: **regular**, **compact**
+
+> Depends on `m3e_design` (ThemeExtension with colors/typography/spacing/shapes).
+
+## Monorepo Layout
+
+```
+packages/
+  m3e_design/
+  button_m3e/
+```
+
+In `pubspec.yaml` this package references `../m3e_design`.
+
+## Usage
+
+```dart
+import 'package:button_m3e/button_m3e.dart';
+
+ButtonM3E(
+  variant: ButtonM3EVariant.filled,
+  size: ButtonM3ESize.medium,
+  labelText: 'Continue',
+  leading: const Icon(Icons.arrow_forward),
+  onPressed: () {},
+);
+```
+
+Full-width button:
+
+```dart
+const ButtonM3E(
+  variant: ButtonM3EVariant.tonal,
+  size: ButtonM3ESize.large,
+  labelText: 'Buy now',
+  expand: true,
+);
+```
+
+Outlined/Text/Elevated work similarly.
+
+## Theming via `m3e_design`
+
+`button_m3e` reads tokens from your theme:
+
+- `m3e.colors.*` for background/foreground/border/disabled
+- `m3e.type.labelLarge` for the button label
+- `m3e.shapes.round|square` (uses `.lg` radius for buttons)
+- `m3e.spacing` for horizontal paddings (`sm`, `md`, `lg`)
+
+If the extension is not present, it falls back to `M3ETheme.defaults(ColorScheme)`.  
+You can still override `ThemeData.colorScheme` to influence defaults globally.
+
+## Notes
+
+- Label can be provided as `labelText` (String) or `label` (Widget).
+- `leading`/`trailing` are optional helpers for icons.
+- `expand: true` makes the button take full width.
+- `density: compact` slightly reduces height for each size.
+
+## License
+
+MIT