chore: add Biome for lint and fix all lint errors

- Install @biomejs/biome as devDependency at root
- Configure biome.json with 2-space indent, double quotes, Tailwind CSS support
- Add lint/lint:fix/format/format:fix scripts to root and app package.json
- Fix noNonNullAssertion: env vars extracted to variables with suppression, <div role=button> replaced with <button>
- Fix noUnusedVariables: remove unused destructured vars
- Fix useIterableCallbackReturn: arrow functions with block body
- Fix noExplicitAny: recharts Tooltip formatters
- Fix noLabelWithoutControl: add htmlFor+id or use <span> for non-input labels
- Fix noStaticElementInteractions/useKeyWithClickEvents: role+keyboard events for overlays
- Fix noArrayIndexKey: use error string as key
- Fix CSS parse: enable tailwindDirectives parser
- Normalize formatting across 80 files with biome check --write

apps/frontend/index.html

@@ -5,7 +5,7 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>Personal Admin</title>
     <script>
-      (function() {
+      (() => {
         var theme = localStorage.getItem("theme");
         if (theme === "dark" || (theme !== "light" && window.matchMedia("(prefers-color-scheme: dark)").matches)) {
           document.documentElement.classList.add("dark");