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/pages/api/views/[slug].ts

@@ -0,0 +1,16 @@
+import type { APIRoute } from 'astro';
+import { getPosts } from '../../../lib/posts';
+import { clientIp, isBot, recordView } from '../../../lib/views';
+
+export const prerender = false;
+
+// POST /api/views/<slug>/ — counts one view (sent with navigator.sendBeacon).
+export const POST: APIRoute = async ({ params, request, clientAddress }) => {
+  const slug = params.slug ?? '';
+  const posts = await getPosts();
+  if (!posts.some((p) => p.id === slug)) return new Response(null, { status: 404 });
+  if (!isBot(request.headers.get('user-agent'))) {
+    recordView(slug, clientIp(request, clientAddress));
+  }
+  return new Response(null, { status: 204, headers: { 'Cache-Control': 'no-store' } });
+};

src/pages/api/views/top.ts

@@ -0,0 +1,19 @@
+import type { APIRoute } from 'astro';
+import { getPosts, postUrl } from '../../../lib/posts';
+import { topViews } from '../../../lib/views';
+
+export const prerender = false;
+
+// GET /api/views/top/?limit=3 — most viewed published posts.
+export const GET: APIRoute = async ({ url }) => {
+  const limit = Math.min(10, Math.max(1, Number(url.searchParams.get('limit')) || 3));
+  const posts = new Map((await getPosts()).map((p) => [p.id, p]));
+  const items = topViews(limit * 2) // headroom for deleted/draft slugs
+    .filter((v) => posts.has(v.slug))
+    .slice(0, limit)
+    .map((v) => {
+      const post = posts.get(v.slug)!;
+      return { slug: v.slug, title: post.data.title, url: postUrl(post), count: v.count };
+    });
+  return Response.json(items, { headers: { 'Cache-Control': 'public, max-age=300' } });
+};