Port AtomCMS atom theme faithfully (Tailwind v4 + real CSS/assets + shell)

Make the template match the atom theme, not just approximate it:
- Add Tailwind v4 (+forms/typography plugins, postcss) and port the real atom
  CSS (global.css + atom app.css) into globals.css: nav-item underline, currency
  + navigation icon classes, site-bg, card-base/hover-lift, text utils — asset
  paths adapted to /assets.
- Copy the real theme assets (backgrounds, icons/currency/navigation, profile,
  leaderboards) into public/assets.
- Rebuild the shell 1:1 from the atom Blade: TopHeader (currency pills +
  user/admin dropdowns, auth-only), SiteHeader (header image + black/50 overlay,
  logo+online+Nitro client / guest Login+Create-account CTA), Navigation (white
  bar, nav-item + Community/Assistance dropdowns), Footer. ThemeVars injects the
  DB-driven CSS custom properties into :root like app.blade.php. Layout uses the
  atom body/site-bg + grid-cols-12 max-w-7xl content wrapper.

Verified: tsc 0, next build exit 0; curl confirms the atom markup, compiled CSS
references the assets, and background-light.jpg + currency/navigation icons all
serve 200.

postcss.config.mjs

@@ -0,0 +1,5 @@
+export default {
+  plugins: {
+    "@tailwindcss/postcss": {},
+  },
+};