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

package.json

@@ -10,6 +10,10 @@
     "astro": "astro"
   },
   "dependencies": {
+    "@astrojs/rss": "^4.0.19",
+    "@astrojs/sitemap": "^3.7.4",
+    "@fontsource-variable/inter": "^5.3.0",
+    "@fontsource/jetbrains-mono": "^5.3.0",
     "astro": "^5.5.0"
   }
 }