[mod] theme/simple: improve fmt/lint tech

This is one of various PR to refactor the simple theme internally.

Replace eslint tool with Biome. I have been using this for quite some time, and
it will help us to have more consistent and valid code without extending on
other third party plugins.

Removes unused dependencies.

package.json

@@ -1,6 +1,5 @@
 {
   "dependencies": {
-    "eslint": "^9.17.0",
     "pyright": "^1.1.391"
   },
   "scripts": {