fix(cursor_gen): satisfy pub publish validation

Add LICENSE (MIT), README, and CHANGELOG for the package root.
Import models.dart in the CLI for OverrideSnapshot.
Wrap tests in main() and add containsNot() helper for analyzer.

Co-authored-by: Cursor <cursoragent@cursor.com>

flutter-cursor-templates/generator/test/generator_test.dart

@@ -95,6 +95,7 @@ final _getxMvcBrief = ProjectBrief(
   locales:         ['en'],
 );
 
+void main() {
 // ─── Resolver tests ─────────────────────────────────────────────────────────
 
 group('Resolver', () {
@@ -343,6 +344,8 @@ group('Golden file tests', () {
   });
 });
 
+}
+
 // ─── Helpers ─────────────────────────────────────────────────────────────────
 
 Future<void> _compareGoldens(String goldenDir, Map<String, String> rendered) async {
@@ -364,9 +367,4 @@ String _templateDir() {
   return script.replaceAll(RegExp(r'test[/\\][^/\\]+$'), '../templates');
 }
 
-// Custom matcher
-Matcher get containsNot => isNot(contains);
-
-extension on Matcher {
-  Matcher call(dynamic value) => isNot(contains(value));
-}
+Matcher containsNot(dynamic expected) => isNot(contains(expected));