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

photos.njk

@@ -59,7 +59,7 @@ permalink: "photos/{% if pagination.pageNumber > 0 %}page/{{ pagination.pageNumb
       {% if post.templateContent %}
       <div class="e-content photo-caption prose dark:prose-invert prose-sm mt-3 max-w-none">{{ post.templateContent | safe }}</div>
       {% endif %}
-      <a class="u-url text-sm text-primary-600 dark:text-primary-400 hover:underline mt-3 inline-block" href="{{ post.url }}">Permalink</a>
+      <a class="u-url text-sm text-purple-600 dark:text-purple-400 hover:underline mt-3 inline-block" href="{{ post.url }}">Permalink</a>
     </li>
     {% endfor %}
   </ul>