WebUI: add linting for regular expressions

And applies to following suggestions:
* Use case-insensitive flag `i`
* Use `\w` for matching characters
* Sort the regex flags

src/webui/www/package.json

@@ -14,6 +14,7 @@
     "@stylistic/eslint-plugin": "*",
     "eslint": "*",
     "eslint-plugin-html": "*",
+    "eslint-plugin-regexp": "*",
     "html-validate": "*",
     "i18next-parser": "*",
     "js-beautify": "*",