Revert m3e_design version to 0.2.0; add theme accessors to simplify retrieval of M3E theme from ThemeData. Update changelog and refactor BuildContext extension with new accessor.

packages/m3e_design/lib/theme/m3e_theme.dart

@@ -97,3 +97,16 @@ class _M3ETypeProxy {
   TextStyle get headlineSmallEmphasized =>
       (_t.base.headlineSmall ?? _empty).merge(_t.emphasized.headline);
 }
+
+// Accessors for getting the M3E theme from ThemeData via Theme.of(context).m3e
+extension M3EThemeAccessors on ThemeData {
+  // Returns the installed M3ETheme; in release builds falls back to defaults
+  M3ETheme get m3e {
+    final e = extension<M3ETheme>();
+    assert(
+      e != null,
+      'M3ETheme is not installed on ThemeData. Wrap your app theme with withM3ETheme(...)',
+    );
+    return e ?? M3ETheme.defaults(colorScheme);
+  }
+}

packages/m3e_design/lib/utils/build_context_x.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
+
 import '../theme/m3e_theme.dart';
 
 extension BuildContextM3EX on BuildContext {
-  M3ETheme get m3e =>
-      Theme.of(this).extension<M3ETheme>() ?? M3ETheme.defaults(Theme.of(this).colorScheme);
+  M3ETheme get m3e => Theme.of(this).m3e;
 }