feat: design-system upgrade + brand to 'Mr Hoelee'

- Extract CSS into src/styles/global.css with design tokens (hoelee.com brand palette)
- Self-hosted Inter + JetBrains Mono via @fontsource
- Sticky nav + manual light/dark toggle + copy-button code blocks
- Author card + Person JSON-LD (E-E-A-T), article meta, related posts, reading time
- Full SEO: canonical, OG (with dims), twitter:card, favicon (all sizes), RSS + sitemap
- New /categories/ and /categories/[category]/ pages
- Add docs/ knowledge guides (content, design, seo, ops) + README index
- Brand name: hoelee.dev -> Mr Hoelee

astro.config.mjs

@@ -1,4 +1,5 @@
 import { defineConfig } from 'astro/config';
+import sitemap from '@astrojs/sitemap';
 
 // https://astro.build/config
 export default defineConfig({
@@ -11,4 +12,5 @@ export default defineConfig({
       prefixDefaultLocale: false,
     },
   },
+  integrations: [sitemap()],
 });