EsLint v9 (#154)

* Upgrade ESLint and related configurations to version 9

- Update ESLint to version 9.19.0
- Migrate ESLint configurations to flat config format
- Remove deprecated ESLint config files
- Update package dependencies and configurations
- Simplify ESLint setup across packages
- Remove unnecessary ESLint config blocks from package.json files
- Improved CI caching with Turborepo tasks
- Removed duplicate styles

packages/email-templates/package.json

@@ -19,16 +19,8 @@
     "@kit/eslint-config": "workspace:*",
     "@kit/i18n": "workspace:*",
     "@kit/prettier-config": "workspace:*",
-    "@kit/tailwind-config": "workspace:*",
     "@kit/tsconfig": "workspace:*"
   },
-  "eslintConfig": {
-    "root": true,
-    "extends": [
-      "@kit/eslint-config/base",
-      "@kit/eslint-config/react"
-    ]
-  },
   "typesVersions": {
     "*": {
       "*": [