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

eslint/index.js

@@ -1,6 +1,10 @@
 'use strict'
 
-module.exports = {
+const plugin = {
+  meta: {
+    name: 'eslint-plugin-bsky-internal',
+    version: '1.0.0',
+  },
   rules: {
     'avoid-unwrapped-text': require('./avoid-unwrapped-text'),
     'use-exact-imports': require('./use-exact-imports'),
@@ -8,3 +12,5 @@ module.exports = {
     'use-prefixed-imports': require('./use-prefixed-imports'),
   },
 }
+
+module.exports = plugin