site: founding post, headline post layout, masonry grid, source links

- New "Why this exists" post; masthead "founded" links to it
- Post template: serif headline + date in masthead, "Filed under {category}" in footer
- Drop counts from footer Collections list
- Masonry component for home + sources grid; source badges link to /sources/#slug
- Theme toggle (settings page + cog) with dark-mode-aware tokens
- Six new themed find lists; cluster-finds skill

src/components/SourceBadge.astro

@@ -1,12 +1,17 @@
 ---
+import { sourceSlug } from '../lib/sources';
+
 interface Props {
   source: string;
   prefix?: string;
 }
 const { source, prefix = 'via' } = Astro.props;
+const href = `/sources/#${sourceSlug(source)}`;
 ---
 
-<span class="source-badge">{prefix} <span class="name">{source}</span></span>
+<span class="source-badge">
+  {prefix} <a href={href} class="name">{source}</a>
+</span>
 
 <style>
   .source-badge {
@@ -25,4 +30,7 @@ const { source, prefix = 'via' } = Astro.props;
     letter-spacing: 0;
     font-weight: 600;
   }
+  .source-badge .name:hover {
+    text-decoration: underline;
+  }
 </style>