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/components/newsletter_form.html

@@ -1,11 +1,12 @@
-<form method="post" action="/newsletter/subscribe/" data-newsletter-form>
+<form method="post" action="/newsletter/subscribe/" data-newsletter-form class="space-y-3" id="newsletter">
   {% csrf_token %}
   <input type="hidden" name="source" value="{{ source|default:'unknown' }}" />
-  <label>
-    <span>{{ label|default:"Newsletter" }}</span>
-    <input type="email" name="email" required />
-  </label>
+  <input type="email" name="email" required placeholder="dev@example.com"
+    class="w-full bg-transparent border border-zinc-300 dark:border-zinc-700 px-4 py-2 text-brand-dark dark:text-brand-light font-mono text-sm focus:outline-none focus:border-brand-pink transition-colors" />
   <input type="text" name="honeypot" style="display:none" />
-  <button type="submit">Subscribe</button>
-  <p data-newsletter-message aria-live="polite"></p>
+  <button type="submit"
+    class="w-full bg-brand-dark text-brand-light dark:bg-brand-light dark:text-brand-dark font-display font-bold py-2 hover:bg-brand-pink dark:hover:bg-brand-pink hover:text-white transition-colors">
+    {{ label|default:"Subscribe" }}
+  </button>
+  <p data-newsletter-message aria-live="polite" class="font-mono text-xs text-brand-cyan min-h-[1rem]"></p>
 </form>