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

_includes/components/widgets/recent-comments.njk

@@ -15,7 +15,7 @@
           <span class="font-medium">{{ comment.author.name or "Anonymous" }}</span>
           <p class="text-surface-600 dark:text-surface-400 line-clamp-2">{{ comment.content.text | truncate(80) }}</p>
           {% if comment["comment-target"] %}
-          <a href="{{ comment['comment-target'] }}" class="text-xs text-primary-600 dark:text-primary-400 hover:underline">View post</a>
+          <a href="{{ comment['comment-target'] }}" class="text-xs text-accent-600 dark:text-accent-400 hover:underline">View post</a>
           {% endif %}
         </div>
       </div>