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/tailwind.config.js

@@ -1,10 +1,34 @@
 module.exports = {
+  darkMode: 'class',
   content: [
     "../../templates/**/*.html",
-    "../../apps/**/templates/**/*.html"
+    "../../apps/**/templates/**/*.html",
   ],
   theme: {
-    extend: {}
+    extend: {
+      fontFamily: {
+        sans: ['Inter', 'sans-serif'],
+        display: ['Space Grotesk', 'sans-serif'],
+        mono: ['Fira Code', 'monospace'],
+      },
+      colors: {
+        brand: {
+          cyan: '#06b6d4',
+          cyanGlow: 'rgba(6,182,212,0.4)',
+          pink: '#ec4899',
+          dark: '#09090b',
+          light: '#fafafa',
+          surfaceDark: '#18181b',
+          surfaceLight: '#ffffff',
+        },
+      },
+      boxShadow: {
+        'neon-cyan': '0 0 20px rgba(6, 182, 212, 0.3)',
+        'neon-pink': '0 0 20px rgba(236, 72, 153, 0.3)',
+        'solid-dark': '6px 6px 0px 0px #09090b',
+        'solid-light': '6px 6px 0px 0px #e4e4e7',
+      },
+    },
   },
-  plugins: []
+  plugins: [],
 };