feat(migration): complete WordPress migration and UX refinements

- Migrate historical posts, localized assets, and 103 comments
- Colocate media into posts/<slug>/images/ and remove wp-content
- Add native bilingual support for ai-can-change post (English default, /zh variant)
- Support clean taxonomy routing (/category/:category and /tag/:tag)
- Dynamically populate categories and tags in sitemap.xml
- Fix header scroll padding/margin offsets for anchor and reference links
- Constrain image and media widths to prevent content overflow
- Redesign homepage recent posts to 4 compact editorial cards
- Restore valid binary favicon.ico and high-res icon assets
- Remove placeholder content and sample test comments

sample-content/posts/hello-world/index.md

@@ -0,0 +1,9 @@
+---
+title: "STSD: Stop Talking Start Doing"
+date: 2016-10-26
+author: "Pengzhan Hao"
+category: "Non-tech"
+tags: []
+cover: "/posts-assets/hello-world/images/cover.webp"
+---
+