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/CHANGELOG.md

@@ -0,0 +1,7 @@
+# Changelog
+
+## 1.0.0
+
+- Initial published release of the `cursor_gen` CLI.
+- Generates `.cursor/` rules and related config from `project-brief.yaml`.
+- Supports validate, generate, refresh (preserve customizations), diff preview, wizard, and update checks.