[script] Add yarn generate-changelog

(disclaimer: I used codex to write this script)

Adds a new `yarn generate-changelog` script to simplify the process of writing changelogs.  You can use it as follows:

```
$ yarn generate-changelog --help

Usage: yarn generate-changelog [--codex|--claude] [--debug] [<pkg@version> ...]

Options:
  --codex     Use Codex for commit summarization.                      [boolean]
  --claude    Use Claude for commit summarization.                     [boolean]
  --debug     Enable verbose debug logging.           [boolean] [default: false]
  -h, --help  Show help                                                [boolean]

Examples:
  generate-changelog --codex                Generate changelog for a single
  eslint-plugin-react-hooks@7.0.1           package using Codex.
  generate-changelog --claude react@19.3    Generate changelog entries for
  react-dom@19.3                            multiple packages using Claude.
  generate-changelog --codex                Generate changelog for all stable
                                            packages using recorded versions.
```

For example, if no args are passed, the script will print find all the relevant commits affecting packages (defaults to `stablePackages` in `ReactVersions.js`) and format them as a simple markdown list.

```
$ yarn generate-changelog

## eslint-plugin-react-hooks@7.0.0
* [compiler] improve zod v3 backwards compat (#34877) ([#34877](#34877) by [@henryqdineen](https://github.com/henryqdineen))
* [ESLint] Disallow passing effect event down when inlined as a prop (#34820) ([#34820](#34820) by [@jf-eirinha](https://github.com/jf-eirinha))
* Switch to `export =` to fix eslint-plugin-react-hooks types (#34949) ([#34949](#34949) by [@karlhorky](https://github.com/karlhorky))
* [eprh] Type `configs.flat` more strictly (#34950) ([#34950](#34950) by [@poteto](https://github.com/poteto))
* Add hint for Node.js cjs-module-lexer for eslint-plugin-react-hook types (#34951) ([#34951](#34951) by [@karlhorky](https://github.com/karlhorky))
* Add hint for Node.js cjs-module-lexer for eslint-plugin-react-hook types (#34953) ([#34953](#34953) by [@karlhorky](https://github.com/karlhorky))

// etc etc...
```

If `--codex` or `--claude` is passed, the script will attempt to use them to summarize the commit(s) in the same style as our existing CHANGELOG.md.

And finally, for debugging the script you can add `--debug` to see what's going on.

Author: poteto

package.json

@@ -152,6 +152,7 @@
     "download-build-in-codesandbox-ci": "yarn build --type=node react/index react.react-server react-dom/index react-dom/client react-dom/src/server react-dom/test-utils react-dom.react-server scheduler/index react/jsx-runtime react/jsx-dev-runtime react-server-dom-webpack",
     "check-release-dependencies": "node ./scripts/release/check-release-dependencies",
     "generate-inline-fizz-runtime": "node ./scripts/rollup/generate-inline-fizz-runtime.js",
+    "generate-changelog": "node ./scripts/tasks/generate-changelog.js",
     "flags": "node ./scripts/flags/flags.js"
   },
   "resolutions": {