Add changelog and release notes

Author: alexeyr

CHANGELOG.md

@@ -35,6 +35,7 @@ Changes since the last non-beta release.
 
 ### Changed
 
+- **Breaking change**: The package is ESM-only now. Please see [Release Notes](docs/release-notes/15.0.0.md#esm-only-package) for more details.
 - The global context is now accessed using `globalThis`. [PR 1727](https://github.com/shakacode/react_on_rails/pull/1727) by [alexeyr-ci2](https://github.com/alexeyr-ci2).
 
 ### [15.0.0-alpha.2] - 2025-03-07

docs/release-notes/15.0.0.md

@@ -68,6 +68,15 @@ Major improvements to component and store hydration:
 - If you were previously using `defer_generated_component_packs: false`, use `generated_component_packs_loading_strategy: :sync` instead
 - For optimal performance with Shakapacker ≥ 8.2.0, consider using `generated_component_packs_loading_strategy: :async`
 
+### ESM-only package
+
+The package is now published as ES Modules instead of CommonJS. In most cases it shouldn't affect your code, as bundlers will be able to handle it. However:
+
+- If you explicitly use `require('react-on-rails')`, and can't change to `import`, upgrade to Node v20.19.0+ or v22.12.0+. They allow `require` for ESM modules without any flags. Node v20.17.0+ may also work, but needs `--experimental-require-module`.
+- If you run into `TS1479: The current file is a CommonJS module whose imports will produce 'require' calls; however, the referenced file is an ECMAScript module and cannot be imported with 'require'.` TypeScript error, you'll need to [upgrade to TypeScript 5.8 and set `module` to `nodenext`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-8.html#support-for-require-of-ecmascript-modules-in---module-nodenext).
+
+Finally, if everything else fails, please contact us and we'll help you upgrade or release a dual ESM-CJS package.
+
 ### `globalThis`
 
 [`globalThis`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis) is now used in code.