feat: replace all primary (blue) with contextual colors across entire theme

Eliminate monotonous blue by replacing ~290 primary- references in 60 files
with semantically appropriate colors:

- accent (teal): links, CTAs, buttons, tabs, focus rings, spinners
- purple: Funkwhale/music, photos, Mastodon/fediverse
- surface (neutral): GitHub, dates/metadata, info boxes
- amber: bookmarks, blogroll categories
- red: likes
- green: reposts
- sky: replies
- orange: RSS/feeds, podcasts
- #0085ff: Bluesky brand
- #a730b8: Mastodon brand

Also updates prose link colors in tailwind.config.js, pagefind UI
primary color to teal, and client-side JS color references.

Confab-Link: http://localhost:8080/sessions/bd3f7012-c703-47e9-bfe2-2ad04ce1842d

search.njk

@@ -14,7 +14,7 @@ pagefindIgnore: true
 <noscript>
   <div class="p-6 bg-surface-100 dark:bg-surface-800 rounded-lg mt-4">
     <p class="text-surface-700 dark:text-surface-300">Search requires JavaScript to be enabled. Please enable JavaScript in your browser settings to use the search feature.</p>
-    <p class="text-surface-500 text-sm mt-2">Alternatively, you can browse content via the <a href="/blog/" class="text-primary-600 dark:text-primary-400 hover:underline">blog archive</a> or <a href="/categories/" class="text-primary-600 dark:text-primary-400 hover:underline">categories</a>.</p>
+    <p class="text-surface-500 text-sm mt-2">Alternatively, you can browse content via the <a href="/blog/" class="text-accent-600 dark:text-accent-400 hover:underline">blog archive</a> or <a href="/categories/" class="text-accent-600 dark:text-accent-400 hover:underline">categories</a>.</p>
   </div>
 </noscript>