chore: sync upstream — performance, webmentions v2, OG v3

- _data: switch to cachedFetch wrapper (10s timeout + 4h watch cache)
- js/webmentions.js: owner reply threading, platform provenance badges, DOM dedup, Micropub reply support
- js/comments.js: owner detection, reply system, Alpine.store integration
- _includes/components/webmentions.njk: data-wm-* attrs, provenance badge slots, reply buttons
- _includes/components/comments.njk: owner-aware comment form, threaded replies
- widgets/toc.njk: Alpine.js tocScanner upgrade (replaces is-land/inline-JS)
- lib/og.js + og-cli.js: OG card v3 (light theme, avatar, batched spawn, DESIGN_VERSION=3)
- eleventy.config.js: hasOgImage cache, memoized date filters, batched OG/unfurl, post-build GC, YouTube check opt
- base.njk: Inter font preloads + toc-scanner.js script
- critical.css: font-face declarations (font-display:optional)
- tailwind.css: font-display swap→optional
- tailwind.config.js: prose link colors -700→-600
- Color design system: accent-700/300 → accent-600/400 across components

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

featured.njk

@@ -121,7 +121,7 @@ permalink: "featured/{% if pagination.pageNumber > 0 %}page/{{ pagination.pageNu
       {% if post.templateContent %}
       <p class="p-summary text-surface-700 dark:text-surface-300 mt-3">{{ post.templateContent | striptags | truncate(250) }}</p>
       {% endif %}
-      <a href="{{ post.url }}" class="text-sm text-accent-700 dark:text-accent-300 hover:underline mt-3 inline-block">Read more &rarr;</a>
+      <a href="{{ post.url }}" class="text-sm text-accent-600 dark:text-accent-400 hover:underline mt-3 inline-block">Read more &rarr;</a>
 
       {% else %}
       {# ── Note ── #}
@@ -137,7 +137,7 @@ permalink: "featured/{% if pagination.pageNumber > 0 %}page/{{ pagination.pageNu
       <div class="e-content prose dark:prose-invert prose-sm mt-3 max-w-none">{{ post.templateContent | safe }}</div>
       {% endif %}
       <div class="post-footer mt-3">
-        <a href="{{ post.url }}" class="text-sm text-accent-700 dark:text-accent-300 hover:underline" aria-label="Permalink: {{ post.data.title or ('Post from ' + (post.date | dateDisplay)) }}">Permalink</a>
+        <a href="{{ post.url }}" class="text-sm text-accent-600 dark:text-accent-400 hover:underline" aria-label="Permalink: {{ post.data.title or ('Post from ' + (post.date | dateDisplay)) }}">Permalink</a>
       </div>
       {% endif %}