build: update npm dependencies (#689)

## Summary

Update all direct npm dependencies and devDependencies to the current
npm latest versions and pin them exactly instead of using caret or tilde
ranges.

## Changes

- Pin all direct runtime and development package versions in
`package.json` and refresh `package-lock.json`.
- Migrate ESLint from `.eslintrc.json` to flat config for ESLint 10.
- Update Jest and TypeScript configuration and test mocks to support the
latest ESM-only packages.
- Add response status handling and typed JSON access for the latest
`node-fetch` types.

## Checklist

- [x] I have read the latest README and followed the instructions.
- [x] I have added or updated tests for behavior changes.
- [x] I have updated README.md and action.yml when inputs or runtime
behavior changed.
- [x] I have run the relevant verification commands.

## Verification

- [x] `npm --userconfig=/private/tmp/empty-npmrc outdated --json
--include=dev` returned `{}`
- [x] `npm run all`
- [x] `npm run build`


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Tests**
* Added comprehensive test mocks for Actions APIs and fetch, improved
integration tests, and updated assertions for more precise error
validation.
  * Configured Jest to map external modules to local test mocks.

* **Chores**
* Migrated ESLint to the flat config format and replaced prior ESLint
config.
* Updated project dependencies and modernized TypeScript compiler
settings.

* **Refactor**
* Adjusted exported tool constants and made error handling more explicit
in version-fetching logic.

[![Review Change
Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/peaceiris/actions-hugo/pull/689)
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Codex <noreply@openai.com>

eslint.config.js

@@ -0,0 +1,40 @@
+const tseslint = require('@typescript-eslint/eslint-plugin');
+const jest = require('eslint-plugin-jest');
+
+const globals = {
+  Atomics: 'readonly',
+  Buffer: 'readonly',
+  SharedArrayBuffer: 'readonly',
+  __dirname: 'readonly',
+  clearTimeout: 'readonly',
+  console: 'readonly',
+  exports: 'writable',
+  module: 'readonly',
+  process: 'readonly',
+  require: 'readonly',
+  setTimeout: 'readonly'
+};
+
+module.exports = [
+  {
+    ignores: ['lib/**', 'coverage/**', 'node_modules/**']
+  },
+  ...tseslint.configs['flat/recommended'],
+  {
+    files: ['src/**/*.ts', '__tests__/**/*.ts'],
+    languageOptions: {
+      ecmaVersion: 2019,
+      sourceType: 'module',
+      globals
+    }
+  },
+  {
+    files: ['__tests__/**/*.ts'],
+    ...jest.configs['flat/recommended'],
+    settings: {
+      jest: {
+        version: 30
+      }
+    }
+  }
+];