feat: add blog with archives, pagination, search, sharing and RSS

- Content collection (one folder per post) with zod schema
- /blog, category and tag archives with /sayfa/<n>/ pagination
- Post page: breadcrumbs, date badges, share bar, TOC, DIY notice,
  code copy, license line, prev/next, BlogPosting + BreadcrumbList JSON-LD
- Sidebar: Pagefind search, categories, featured fallback, tag cloud
- Sätteri HAST plugins for figure/figcaption and external links
- Dual-theme Shiki, themed prose, RSS feed, latest posts on home
- Three sample posts marked as examples

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

src/components/blog/DateBadges.astro

@@ -0,0 +1,41 @@
+---
+import { blog, fmt } from '../../lib/data';
+import { dateBadges, formatDate, isoDay, type DateBadge } from '../../lib/dates';
+import Badge from '../Badge.astro';
+
+export interface Props {
+  pubDate: Date;
+  updatedDate?: Date;
+  /** Reading time in minutes, shown after the dates. */
+  minutes?: number;
+  class?: string;
+}
+
+const { pubDate, updatedDate, minutes, class: className } = Astro.props;
+const { primary, secondary } = dateBadges(pubDate, updatedDate);
+
+const meta = (b: DateBadge) =>
+  b.kind === 'updated'
+    ? { label: blog.dates.updated, icon: 'tabler:refresh' }
+    : { label: blog.dates.created, icon: 'tabler:calendar-plus' };
+const p = meta(primary);
+const s = secondary && meta(secondary);
+---
+
+<div class:list={['flex flex-wrap items-center gap-2', className]}>
+  <Badge variant="solid" icon={p.icon}>
+    {p.label}
+    <time datetime={isoDay(primary.date)}>{formatDate(primary.date)}</time>
+  </Badge>
+  {secondary && s && (
+    <Badge variant="outline" icon={s.icon}>
+      {s.label}
+      <time datetime={isoDay(secondary.date)}>{formatDate(secondary.date)}</time>
+    </Badge>
+  )}
+  {minutes && (
+    <Badge variant="outline" icon="tabler:clock">
+      {fmt(blog.card.readingTime, { n: minutes })}
+    </Badge>
+  )}
+</div>