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/app_bar_m3e/README.md

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+# app_bar_m3e
+
+Expressive **App Bar** for Flutter (Material 3 Expressive).  
+Small (standard) bar for `Scaffold.appBar`, plus **Medium** & **Large** collapsing variants via a sliver.
+
+> Uses `m3e_design` tokens for color, typography, spacing, and shapes.
+
+## Monorepo Setup
+
+Place alongside `m3e_design` in your repo:
+
+```
+packages/
+  m3e_design/
+  app_bar_m3e/
+```
+
+`pubspec.yaml` references `../m3e_design` by default.
+
+## API
+
+### Small App Bar
+
+```dart
+AppBarM3E(
+  leading: IconButton(icon: const BackButtonIcon(), onPressed: () {}),
+  titleText: 'Inbox',
+  actions: [IconButton(icon: const Icon(Icons.search), onPressed: () {})],
+  centerTitle: false,
+  shapeFamily: AppBarM3EShapeFamily.round,
+  density: AppBarM3EDensity.regular,
+);
+```
+
+Use in a `Scaffold`:
+
+```dart
+Scaffold(
+  appBar: const AppBarM3E(titleText: 'Inbox'),
+  body: ...
+);
+```
+
+### Sliver App Bar (Medium / Large)
+
+```dart
+CustomScrollView(
+  slivers: [
+    SliverAppBarM3E(
+      variant: AppBarM3EVariant.large,
+      titleText: 'Gallery',
+      pinned: true,
+    ),
+    // ... content slivers
+  ],
+);
+```
+
+- `variant: medium` uses expanded height ≈112dp (collapses to ~64dp).
+- `variant: large` uses expanded height ≈152dp (collapses to ~64dp).
+- Colors, shapes, and typography come from `m3e_design`'s `M3ETheme` extension.
+
+## Theme Integration
+
+`app_bar_m3e` reads the `M3ETheme` extension from your `ThemeData`:
+
+```dart
+final m3e = Theme.of(context).extension<M3ETheme>() ??
+            M3ETheme.defaults(Theme.of(context).colorScheme);
+```
+
+It uses:
+- `m3e.colors.surfaceContainerHigh` for background
+- `m3e.type.titleLarge` for collapsed titles
+- `m3e.type.headlineSmallEmphasized` for expanded titles
+- `m3e.shapes.round|square` for container shape
+- `m3e.spacing.md` for horizontal padding
+
+Override by supplying `backgroundColor`, `foregroundColor`, `toolbarHeight`, etc.
+
+## Notes
+
+- For collapsing behavior, use the sliver variant inside a `CustomScrollView`.
+- `AppBarM3E` (small) is a `PreferredSizeWidget` suitable for `Scaffold.appBar`.
+- Medium/Large variants rely on `FlexibleSpaceBar` for expanded titles.
+- When `density: compact`, default heights reduce by ~8dp.
+
+## License
+
+MIT