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/navigation_bar_m3e/README.md

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+# navigation_bar_m3e
+
+Material 3 **Expressive** Navigation Bar for Flutter with badges, pill/underline indicators, and token-driven styling.
+
+- `NavigationBarM3E` — wrapper around Flutter's `NavigationBar` with M3E tokens
+- `NavigationDestinationM3E` — destination data (icon, selectedIcon, label, badge)
+- `NavBadgeM3E` — small badge/dot utility for icons
+
+All styling is driven by the `m3e_design` ThemeExtension (**M3ETheme**).
+
+## Monorepo Layout
+
+```
+packages/
+  m3e_design/
+  navigation_bar_m3e/
+```
+
+`pubspec.yaml` references `../m3e_design`.
+
+## Usage
+
+```dart
+import 'package:navigation_bar_m3e/navigation_bar_m3e.dart';
+
+final items = [
+  const NavigationDestinationM3E(
+    icon: Icon(Icons.home_outlined),
+    selectedIcon: Icon(Icons.home),
+    label: 'Home',
+  ),
+  const NavigationDestinationM3E(
+    icon: Icon(Icons.search),
+    label: 'Search',
+    badgeCount: 3,
+  ),
+  const NavigationDestinationM3E(
+    icon: Icon(Icons.person),
+    label: 'Profile',
+    badgeDot: true,
+  ),
+];
+
+NavigationBarM3E(
+  destinations: items,
+  selectedIndex: 0,
+  onDestinationSelected: (i) {},
+  labelBehavior: NavBarM3ELabelBehavior.onlySelected,
+  indicatorStyle: NavBarM3EIndicatorStyle.pill, // pill | underline | none
+  size: NavBarM3ESize.medium,
+  density: NavBarM3EDensity.regular,
+  shapeFamily: NavBarM3EShapeFamily.round,
+);
+```
+
+## Tokens mapping
+
+- **Container**: `surfaceContainerHigh`
+- **Indicator**: `secondaryContainer` (color), pill shape by default; `underline` style uses a bottom border
+- **Selected**: `onSecondaryContainer` (icon/label)
+- **Unselected**: `onSurfaceVariant`
+- **Label style**: `labelMedium`
+- **Heights**: `small ≈64dp`, `medium ≈80dp`
+- **Icon size**: `24dp`
+
+## Badges
+
+Use `badgeCount` for numeric badges or `badgeDot: true` for a small dot. Colors default to `errorContainer / onErrorContainer` and can be overridden via `NavBadgeM3E`.
+
+## Accessibility
+
+- Provide `semanticLabel` per destination (used as tooltip) or on the bar.
+- Label behavior options: **alwaysShow**, **onlySelected**, or **alwaysHide**.
+
+## License
+
+MIT