feat: implement Tailwind CSS styling based on wireframe design

- Add brand colours, fonts (Space Grotesk/Inter/Fira Code), box shadows to tailwind.config.js
- Add bg-grid-pattern, text-gradient, scrollbar, selection styles to input.css
- Add Google Fonts link and dark-mode body classes to base.html
- Style nav, footer, cookie banner, newsletter form components
- Style homepage: featured article, 12-col editorial grid, sidebar widgets
- Style article list: header, tag filters, horizontal article cards, pagination
- Style article page: hero header, prose body, share sidebar, related cards, comments
- Style code blocks and callout blocks
- CSS output grows from 4.8KB to 24KB with all brand utilities compiled

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

theme/static_src/src/input.css

@@ -1,3 +1,40 @@
 @tailwind base;
 @tailwind components;
 @tailwind utilities;
+
+@layer utilities {
+  .bg-grid-pattern {
+    background-image: radial-gradient(rgba(0, 0, 0, 0.1) 1px, transparent 1px);
+    background-size: 24px 24px;
+  }
+  .dark .bg-grid-pattern {
+    background-image: radial-gradient(rgba(255, 255, 255, 0.07) 1px, transparent 1px);
+  }
+  .text-gradient {
+    background: linear-gradient(135deg, #06b6d4, #ec4899);
+    -webkit-background-clip: text;
+    -webkit-text-fill-color: transparent;
+    background-clip: text;
+  }
+}
+
+::selection {
+  background-color: #ec4899;
+  color: #ffffff;
+}
+
+pre {
+  scrollbar-width: thin;
+  scrollbar-color: rgba(156, 163, 175, 0.5) transparent;
+}
+pre::-webkit-scrollbar {
+  height: 6px;
+}
+pre::-webkit-scrollbar-thumb {
+  background-color: rgba(156, 163, 175, 0.5);
+  border-radius: 3px;
+}
+
+body {
+  transition: background-color 0.3s ease, color 0.3s ease;
+}