chore(repo): migrate nx repo to eslint v9 flat config (#35359)

## Current Behavior

The nx repo uses the legacy eslintrc format (`.eslintrc.json`,
`.eslintignore`) with ESLint v8 and outdated plugin versions. Several of
those plugins ship code that crashes under ESLint v9 (`context.getScope`
removed, etc.), and the `@nx/eslint` / `@nx/eslint-plugin` sources still
reference APIs removed in v9 (`Linter.defineParser`,
`Linter.defineRule`, classic `Linter.Config` shape).

## Expected Behavior

Every project in the repo uses an `eslint.config.mjs` flat config, the
ESLint ecosystem is on the latest v9-compatible versions, and
`@nx/eslint` / `@nx/eslint-plugin` sources compile and test cleanly
against the v9 type split.

### Main changes

- Replaced every `.eslintrc.json` / `.eslintignore` with an
`eslint.config.mjs`.
- Rewrote the root `eslint.config.mjs`:
- Exports a named `baseConfig` that leaf configs import, plus a default
export that opts out of linting (`**/*` ignored) so the root acts as a
shared base and isn't lint-checked directly.
  - Drops `FlatCompat` in favor of native plugin imports.
- Exports shared `reactHooksV7Off`, `e2eTestOnlyIgnores`, and a
`storybookConfigs` wrapper that filters v10's preset down to
`storybook/*` rules (the preset references foreign rules like
`import-x/*` that we don't register).
- Cleaned up leaf configs emitted by the generator: deduplicated file
entries, merged split `package.json` blocks, fixed the jsonc parser
namespace import after v3 dropped its default export.
- Scoped the 15 e2e projects to `*.test.ts` files only via a shared
export.
- Bumped the ESLint ecosystem to the latest v9-compatible versions:
`eslint@^9.39.4`, `@eslint/js@^9.39.4`, `@typescript-eslint/*@^8.58.2`,
`eslint-plugin-storybook@^10.3.5`, `eslint-plugin-react-hooks@^7.1.0`,
`eslint-plugin-jsx-a11y@^6.10.2`, `eslint-plugin-import@^2.32.0`,
`eslint-plugin-playwright@^2.10.1`, `eslint-plugin-cypress@^6.3.1`,
`eslint-plugin-jest@^29.15.2`, `toml-eslint-parser@^1.0.3`,
`jsonc-eslint-parser@^3.1.0`, `angular-eslint@^21.3.1`. Dropped
`@eslint/eslintrc`, `@types/eslint`, `@types/eslint__js`.
- Aligned `@nx/eslint` source with the v9 type split: `Linter.Config` →
`Linter.LegacyConfig`, `ESLint.Options` → `ESLint.LegacyOptions`
wherever the underlying shape is eslintrc.
- Rewrote `@nx/eslint-plugin` rule specs (`dependency-checks`,
`enforce-module-boundaries`) as flat-config inline tests since
`Linter.defineParser`/`defineRule` were removed in v9.
- Aligned react/angular/expo/react-native add-linting helpers with the
v9 type split.
- Migrated `tools/eslint-rules` specs from `TSESLint.RuleTester` (legacy
config, rejected by v9's flat Linter) to
`@typescript-eslint/rule-tester`; added `isolatedModules: true` so
ts-jest resolves the new types under `module: node16`.
- Downgraded the new react-hooks v7 rules to `off` via a shared export
so the migration doesn't require rewriting legacy code.
- Auto-fixed unused eslint-disable directives
(`linterOptions.reportUnusedDisableDirectives` defaults to warn in v9).
- Ignored `packages/workspace/**/__fixtures__/**` in lint and updated
the affected snapshot so the fixture matches what the jest generator
templates actually emit.

### Note on ESLint v10

This PR stays on ESLint v9. A few plugins we rely on
(`eslint-plugin-import`, `eslint-plugin-jsx-a11y`,
`eslint-plugin-react`) still don't declare v10 peer support. The jump to
v10 will happen in a follow-up PR once those plugins publish
v10-compatible releases.

Author: leosvelperez

.eslintignore

@@ -0,0 +1,23 @@
+import { baseConfig } from '../eslint.config.mjs';
+import playwright from 'eslint-plugin-playwright';
+
+export default [
+  ...baseConfig,
+  playwright.configs['flat/recommended'],
+  {
+    files: ['**/*.spec.ts', '**/*.test.ts', '**/*.spec.js', '**/*.test.js'],
+    rules: {
+      'playwright/no-standalone-expect': 'off',
+    },
+  },
+  {
+    ignores: [
+      'node_modules/',
+      'dist/',
+      '.astro/',
+      '.netlify/',
+      'test-output/',
+      'playwright-report/',
+    ],
+  },
+];

.eslintrc.json

@@ -0,0 +1,3 @@
+import { baseConfig, e2eTestOnlyIgnores } from '../../eslint.config.mjs';
+
+export default [...baseConfig, e2eTestOnlyIgnores];

astro-docs/.eslintignore

@@ -0,0 +1,3 @@
+import { baseConfig, e2eTestOnlyIgnores } from '../../eslint.config.mjs';
+
+export default [...baseConfig, e2eTestOnlyIgnores];