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

lib/unfurl-shortcode.js

@@ -105,7 +105,7 @@ export function renderCard(url, metadata) {
     ? `<img src="${escapeHtml(favicon)}" alt="" class="inline-block w-4 h-4 mr-1 align-text-bottom" loading="lazy" />`
     : "";
 
-  return `<div class="unfurl-card not-prose my-4 rounded-lg border border-surface-200 dark:border-surface-700 bg-surface-50 dark:bg-surface-800 overflow-hidden hover:border-primary-300 dark:hover:border-primary-600 transition-colors">
+  return `<div class="unfurl-card not-prose my-4 rounded-lg border border-surface-200 dark:border-surface-700 bg-surface-50 dark:bg-surface-800 overflow-hidden hover:border-accent-300 dark:hover:border-accent-600 transition-colors">
   <a href="${escapeHtml(url)}" rel="noopener" target="_blank" class="flex no-underline text-inherit hover:text-inherit">
     <div class="flex-1 p-3 sm:p-4 min-w-0">
       <p class="font-semibold text-sm sm:text-base text-surface-900 dark:text-surface-100 truncate m-0">${escapeHtml(title)}</p>