feat: add anonymous view counter with most-read sidebar

- node:sqlite storage in $DATA_DIR/views.db (no native deps)
- POST /api/views/<slug>/ counts once per visitor per 24h via
  daily-salted hash; IPs are never stored, bots are skipped
- GET /api/views/top/ feeds the sidebar's featured list, falling back
  to frontmatter-featured and latest posts when unavailable

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/components/blog/Sidebar.astro

@@ -71,9 +71,9 @@ const title = 'font-display mb-4 flex items-center gap-3 text-sm font-bold track
         {blog.sidebar.featured}
         <span aria-hidden="true" class="bg-accent h-0.5 w-8"></span>
       </h2>
-      <ol data-featured class="flex flex-col gap-4">
+      <ol data-featured data-limit="3" class="flex flex-col gap-4">
         {featured.map((post, i) => (
-          <li class="flex gap-3">
+          <li class="flex gap-3" data-slug={post.id}>
             <span
               aria-hidden="true"
               class="font-display text-accent-text text-2xl leading-none font-black"
@@ -115,3 +115,37 @@ const title = 'font-display mb-4 flex items-center gap-3 text-sm font-bold track
     </section>
   )}
 </aside>
+
+<script>
+  // Replace the build-time fallback with the most viewed posts when the API is reachable.
+  const list = document.querySelector<HTMLOListElement>('ol[data-featured]');
+  if (list) {
+    const limit = Number(list.dataset.limit) || 3;
+    fetch(`/api/views/top/?limit=${limit}`)
+      .then((r) => (r.ok ? r.json() : []))
+      .then((top: { slug: string; title: string; url: string }[]) => {
+        if (!top.length) return;
+        const template = list.querySelector('li');
+        if (!template) return;
+        const fallback = [...list.querySelectorAll<HTMLLIElement>('li')];
+        const items = top.map((t) => {
+          const li = template.cloneNode(true) as HTMLLIElement;
+          li.dataset.slug = t.slug;
+          const a = li.querySelector('a')!;
+          a.href = t.url;
+          a.textContent = t.title;
+          return li;
+        });
+        // Top up with fallback posts not already listed.
+        for (const li of fallback) {
+          if (items.length >= limit) break;
+          if (!items.some((x) => x.dataset.slug === li.dataset.slug)) items.push(li);
+        }
+        items.forEach((li, i) => {
+          li.querySelector('span')!.textContent = String(i + 1).padStart(2, '0');
+        });
+        list.replaceChildren(...items);
+      })
+      .catch(() => {});
+  }
+</script>