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>

templates/blog/blocks/code_block.html

@@ -1,5 +1,19 @@
 {% load wagtailcore_tags %}
-<div class="code-block">
-  {% if value.filename %}<div>{{ value.filename }}</div>{% endif %}
-  <pre data-lang="{{ value.language }}"><code class="language-{{ value.language }}">{{ value.raw_code }}</code></pre>
+<div class="my-8 overflow-hidden bg-[#0d1117] border border-zinc-800 shadow-xl">
+  <div class="flex items-center justify-between px-4 py-2 bg-[#161b22] border-b border-zinc-800">
+    <div class="flex gap-2">
+      <div class="w-3 h-3 rounded-full bg-red-500"></div>
+      <div class="w-3 h-3 rounded-full bg-yellow-500"></div>
+      <div class="w-3 h-3 rounded-full bg-green-500"></div>
+    </div>
+    {% if value.filename %}
+      <div class="font-mono text-xs text-zinc-500">{{ value.filename }}</div>
+    {% else %}
+      <div class="font-mono text-xs text-zinc-500">{{ value.language }}</div>
+    {% endif %}
+    <div class="w-8"></div>
+  </div>
+  <div class="overflow-x-auto">
+    <pre data-lang="{{ value.language }}" class="p-6 text-sm"><code class="language-{{ value.language }} font-mono text-zinc-300">{{ value.raw_code }}</code></pre>
+  </div>
 </div>