Switch project styles from SCSS to CSS and add Tailwind

Replaces SCSS files with CSS equivalents, updates Angular configuration to use CSS for styles, and adds Tailwind CSS with PostCSS integration. Updates dependencies in package.json and package-lock.json to include tailwindcss, postcss, and related plugins. The app.html template is replaced with a minimal version, removing the previous placeholder content.

.postcssrc.json

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