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/m3e_design/lib/theme/m3e_theme.dart

@@ -0,0 +1,99 @@
+import 'package:flutter/material.dart';
+
+import '../tokens/color_tokens.dart';
+import '../tokens/motion_tokens.dart';
+import '../tokens/shape_tokens.dart';
+import '../tokens/spacing_tokens.dart';
+import '../tokens/typography_tokens.dart';
+
+@immutable
+class M3ETheme extends ThemeExtension<M3ETheme> {
+  final M3EColors colors;
+  final M3ETypography typography;
+  final M3EShapes shapes;
+  final M3ESpacing spacing;
+  final M3EMotion motion;
+
+  const M3ETheme({
+    required this.colors,
+    required this.typography,
+    required this.shapes,
+    required this.spacing,
+    required this.motion,
+  });
+
+  // Convenience proxy for commonly used text styles in packages (m3e.type.*)
+  _M3ETypeProxy get type => _M3ETypeProxy(typography);
+
+  static M3ETheme defaults(ColorScheme scheme) => M3ETheme(
+        colors: M3EColors.from(scheme),
+        typography: M3ETypography.defaultFor(scheme.brightness),
+        shapes: M3EShapes.expressive(),
+        spacing: const M3ESpacing.regular(),
+        motion: const M3EMotion.expressive(),
+      );
+
+  @override
+  M3ETheme copyWith({
+    M3EColors? colors,
+    M3ETypography? typography,
+    M3EShapes? shapes,
+    M3ESpacing? spacing,
+    M3EMotion? motion,
+  }) =>
+      M3ETheme(
+        colors: colors ?? this.colors,
+        typography: typography ?? this.typography,
+        shapes: shapes ?? this.shapes,
+        spacing: spacing ?? this.spacing,
+        motion: motion ?? this.motion,
+      );
+
+  @override
+  M3ETheme lerp(covariant M3ETheme? other, double t) {
+    if (other == null) return this;
+    return M3ETheme(
+      colors: M3EColors.lerp(colors, other.colors, t),
+      typography: M3ETypography.lerp(typography, other.typography, t),
+      shapes: M3EShapes.lerp(shapes, other.shapes, t),
+      spacing: M3ESpacing.lerp(spacing, other.spacing, t),
+      motion: M3EMotion.lerp(motion, other.motion, t),
+    );
+  }
+}
+
+/// Inject (or replace) the M3ETheme extension on a ThemeData.
+ThemeData withM3ETheme(ThemeData base, {M3ETheme? override}) {
+  // Use any existing M3ETheme, else the provided override, else defaults.
+  final current = base.extension<M3ETheme>();
+  final next = override ?? current ?? M3ETheme.defaults(base.colorScheme);
+
+  // Merge existing extensions (values) with our M3ETheme, replacing prior ones.
+  final Iterable<ThemeExtension<dynamic>> existing = base.extensions.values;
+  final List<ThemeExtension<dynamic>> merged = <ThemeExtension<dynamic>>[];
+  for (final e in existing) {
+    if (e is! M3ETheme) {
+      merged.add(e);
+    }
+  }
+  merged.add(next);
+
+  return base.copyWith(extensions: merged);
+}
+
+// Internal proxy for typography shortcuts used by components.
+class _M3ETypeProxy {
+  const _M3ETypeProxy(this._t);
+  final M3ETypography _t;
+
+  TextStyle get _empty => const TextStyle();
+  TextStyle get titleLarge => _t.base.titleLarge ?? _empty;
+  TextStyle get titleSmall => _t.base.titleSmall ?? _empty;
+  TextStyle get bodySmall => _t.base.bodySmall ?? _empty;
+  TextStyle get labelLarge => _t.base.labelLarge ?? _empty;
+  TextStyle get labelMedium => _t.base.labelMedium ?? _empty;
+  TextStyle get labelSmall => _t.base.labelSmall ?? _empty;
+
+  TextStyle get headlineSmallEmphasized =>
+      (_t.base.headlineSmall ?? _empty).merge(_t.emphasized.headline);
+}