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>

astro.config.mjs

@@ -6,6 +6,8 @@ import mdx from '@astrojs/mdx';
 import sitemap from '@astrojs/sitemap';
 import node from '@astrojs/node';
 import icon from 'astro-icon';
+import { satteri } from '@astrojs/markdown-satteri';
+import { externalLinksPlugin, figurePlugin } from './src/lib/markdown-plugins.mjs';
 
 /**
  * Dev-only routes (style preview); never part of a production build.
@@ -29,6 +31,15 @@ export default defineConfig({
   output: 'static',
   adapter: node({ mode: 'standalone' }),
   integrations: [mdx(), sitemap(), icon({ include: { tabler: ['*'] } }), devRoutes],
+  markdown: {
+    processor: satteri({ hastPlugins: [figurePlugin, externalLinksPlugin] }),
+    // Dual themes; colours switch with [data-theme] in global.css.
+    shikiConfig: {
+      themes: { light: 'github-light-high-contrast', dark: 'github-dark-high-contrast' },
+      defaultColor: false,
+      wrap: false,
+    },
+  },
   vite: {
     plugins: [tailwindcss()],
   },