Upgrade ESLint to v9 with flat config

- Upgrade eslint from v8 to v9.18.0
- Migrate from .eslintrc.js to eslint.config.mjs (flat config)
- Upgrade typescript-eslint to v8.20.0 (unified package)
- Replace eslint-plugin-import with eslint-plugin-import-x for flat config support
- Add globals package for environment globals
- Update eslint-plugin-bsky-internal with proper meta objects for ESLint v9
- Fix deprecated context.getScope() API usage
- Update bskyembed to use flat config
- Remove deprecated --ext flag from lint scripts
- Configure rules to maintain previous behavior while using new ESLint version

bskyembed/.eslintrc.cjs

@@ -1,22 +0,0 @@
-module.exports = {
-  root: true,
-  parser: '@typescript-eslint/parser',
-  plugins: ['@typescript-eslint', 'simple-import-sort'],
-  extends: [
-    'eslint:recommended',
-    'preact',
-    'plugin:@typescript-eslint/recommended',
-    'plugin:@typescript-eslint/recommended-requiring-type-checking',
-  ],
-  rules: {
-    'simple-import-sort/imports': 'warn',
-    'simple-import-sort/exports': 'warn',
-    'no-else-return': 'off',
-  },
-  parserOptions: {
-    sourceType: 'module',
-    ecmaVersion: 'latest',
-    project: ['./tsconfig.json'],
-    tsconfigRootDir: __dirname,
-  },
-}

bskyembed/eslint.config.mjs

@@ -0,0 +1,52 @@
+// @ts-check
+import js from '@eslint/js'
+import tseslint from 'typescript-eslint'
+import simpleImportSort from 'eslint-plugin-simple-import-sort'
+import globals from 'globals'
+
+export default tseslint.config(
+  // Global ignores
+  {
+    ignores: ['dist/**', 'node_modules/**'],
+  },
+
+  // Base JS recommended rules
+  js.configs.recommended,
+
+  // TypeScript rules with type checking
+  ...tseslint.configs.recommendedTypeChecked,
+
+  // Main configuration
+  {
+    files: ['**/*.{js,jsx,ts,tsx}'],
+    plugins: {
+      'simple-import-sort': simpleImportSort,
+    },
+    languageOptions: {
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+      globals: {
+        ...globals.browser,
+      },
+      parserOptions: {
+        projectService: true,
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+    rules: {
+      'simple-import-sort/imports': 'warn',
+      'simple-import-sort/exports': 'warn',
+      'no-else-return': 'off',
+      '@typescript-eslint/no-require-imports': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        {
+          argsIgnorePattern: '^_',
+          varsIgnorePattern: '^_',
+          caughtErrors: 'none',
+          ignoreRestSiblings: true,
+        },
+      ],
+    },
+  },
+)

bskyembed/package.json

@@ -7,7 +7,7 @@
     "dev-snippet": "tsc --project tsconfig.snippet.json && serve -s dist -p 3000 -n",
     "build": "tsc && vite build",
     "build-snippet": "tsc --project tsconfig.snippet.json",
-    "lint": "eslint --cache --ext .js,.jsx,.ts,.tsx src",
+    "lint": "eslint --cache src",
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
@@ -17,11 +17,13 @@
   "devDependencies": {
     "@preact/preset-vite": "^2.10.2",
     "@vitejs/plugin-legacy": "^7.0.0",
+    "@eslint/js": "^9.18.0",
     "autoprefixer": "^10.4.19",
-    "eslint": "^8.19.0",
-    "eslint-config-preact": "^1.3.0",
-    "eslint-plugin-simple-import-sort": "^12.0.0",
+    "eslint": "^9.18.0",
+    "eslint-plugin-simple-import-sort": "^12.1.1",
+    "globals": "^15.14.0",
     "postcss": "^8.4.38",
+    "typescript-eslint": "^8.20.0",
     "serve": "^14.2.5",
     "tailwindcss": "^3.4.3",
     "terser": "^5.43.1",