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>

digest-index.njk

@@ -24,7 +24,7 @@ permalink: "digest/{% if pagination.pageNumber > 0 %}page/{{ pagination.pageNumb
     {% for d in paginatedDigests %}
     <li class="p-4 bg-surface-50 dark:bg-surface-800 border border-surface-200 dark:border-surface-700 rounded-lg hover:border-amber-400 dark:hover:border-amber-600 transition-colors shadow-sm">
       <a href="/digest/{{ d.slug }}/" class="block">
-        <h2 class="font-semibold text-surface-900 dark:text-surface-100 hover:text-accent-700 dark:hover:text-accent-300">
+        <h2 class="font-semibold text-surface-900 dark:text-surface-100 hover:text-accent-600 dark:hover:text-accent-400">
           {{ d.label }}
         </h2>
         <p class="text-sm text-surface-600 dark:text-surface-400 mt-1">