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_rail_m3e/README.md

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+# navigation_rail_m3e
+
+Material 3 **Expressive** Navigation Rail for Flutter with badges, pill/stripe indicators, and token-driven styling.
+
+- `NavigationRailM3E` — wrapper around Flutter's `NavigationRail` with M3E tokens
+- `RailDestinationM3E` — destination data (icon, selectedIcon, label, badge)
+- `RailBadgeM3E` — small badge/dot utility for icons
+
+All styling is driven by the `m3e_design` ThemeExtension (**M3ETheme**).
+
+## Monorepo Layout
+
+```
+packages/
+  m3e_design/
+  navigation_rail_m3e/
+```
+
+`pubspec.yaml` references `../m3e_design`.
+
+## Usage
+
+```dart
+import 'package:navigation_rail_m3e/navigation_rail_m3e.dart';
+
+final items = [
+  const RailDestinationM3E(
+    icon: Icon(Icons.inbox_outlined),
+    selectedIcon: Icon(Icons.inbox),
+    label: 'Inbox',
+  ),
+  const RailDestinationM3E(
+    icon: Icon(Icons.chat_bubble_outline),
+    label: 'Chat',
+    badgeCount: 5,
+  ),
+  const RailDestinationM3E(
+    icon: Icon(Icons.settings_outlined),
+    label: 'Settings',
+    badgeDot: true,
+  ),
+];
+
+NavigationRailM3E(
+  destinations: items,
+  selectedIndex: 0,
+  onDestinationSelected: (i) {},
+  labelBehavior: RailLabelBehavior.onlySelected, // none | onlySelected | alwaysShow
+  indicatorStyle: RailIndicatorStyle.pill,       // pill | stripe | none
+  size: RailSize.regular,                        // compact | regular
+  density: RailDensity.regular,                  // regular | compact
+  shapeFamily: RailShapeFamily.round,            // round | square
+  extended: false,                               // true to show labels permanently (wide rail)
+  groupAlignment: -1.0,                          // -1 top .. 1 bottom
+  leading: const Padding(
+    padding: EdgeInsets.all(8.0),
+    child: FlutterLogo(size: 24),
+  ),
+);
+```
+
+## Tokens mapping
+
+- **Container**: `surfaceContainerHigh`
+- **Indicator**: `secondaryContainer` (color). `pill` uses NavigationRail's indicator; `stripe` draws a left border on the selected icon.
+- **Selected**: `onSecondaryContainer` (icon/label)
+- **Unselected**: `onSurfaceVariant`
+- **Label style**: `labelMedium`
+- **Widths**: compact **≈64dp**, regular **≈80dp**, extended min **≈256dp**
+- **Icon size**: **24dp**
+- **Item padding**: from `spacing.sm/md`
+
+## Badges
+
+Use `badgeCount` for numeric badges or `badgeDot: true` for a small dot. Colors default to `errorContainer / onErrorContainer` and can be overridden via `RailBadgeM3E`.
+
+## Accessibility
+
+- Provide `semanticLabel` per destination (used as tooltip) or on the rail (`semanticLabel` on the widget).
+- Choose the label behavior to balance density with readability.
+
+## License
+
+MIT