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

categories-index.njk

@@ -18,7 +18,7 @@ eleventyImport:
   <ul class="flex flex-wrap gap-3">
     {% for cat in collections.categories %}
     <li>
-      <a href="/categories/{{ cat | slugify }}/" class="inline-block px-4 py-2 bg-surface-100 dark:bg-surface-800 text-surface-900 dark:text-surface-100 rounded-lg hover:bg-primary-100 dark:hover:bg-primary-900 hover:text-primary-700 dark:hover:text-primary-300 transition-colors">
+      <a href="/categories/{{ cat | slugify }}/" class="inline-block px-4 py-2 bg-surface-100 dark:bg-surface-800 text-surface-900 dark:text-surface-100 rounded-lg hover:bg-accent-100 dark:hover:bg-accent-900 hover:text-accent-700 dark:hover:text-accent-300 transition-colors">
         {{ cat }}
       </a>
     </li>