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

views/partials/header.ejs

@@ -2,9 +2,6 @@
   <div class="container header-inner">
     <a href="/" class="brand">
       <span class="brand-title"><%= site.title %></span>
-      <% if (site.tagline) { %>
-        <span class="brand-tagline"><%= site.tagline %></span>
-      <% } %>
     </a>
 
     <!-- Desktop Navigation -->