refactor: move tenant templates to internal/tenant

- Move internal/build/ to internal/tenant/
- Rename assets for clarity
- Add tenant-blog.js for shared blog functionality
- Update style.css with improved code block styling

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/build/templates/blog.html

@@ -1,34 +0,0 @@
-{{define "content"}}
-<div class="blog">
-  <header class="blog-header">
-    <h1>Posts</h1>
-  </header>
-
-  <section class="posts-list">
-    {{range .Posts}}
-    <article class="post-card">
-      <a href="/posts/{{.Slug}}">
-        <h2 class="post-card-title">{{.Title}}</h2>
-        <time class="post-card-date" datetime="{{.Date.Format "2006-01-02"}}">{{.Date.Format "January 2, 2006"}}</time>
-        {{if .Description}}
-        <p class="post-card-description">{{.Description}}</p>
-        {{end}}
-      </a>
-    </article>
-    {{else}}
-    <p class="no-posts">No posts yet.</p>
-    {{end}}
-  </section>
-
-  {{if or .PrevPage .NextPage}}
-  <nav class="pagination">
-    {{if .PrevPage}}
-    <a href="{{.PrevPage}}" class="pagination-prev">&larr; Newer</a>
-    {{end}}
-    {{if .NextPage}}
-    <a href="{{.NextPage}}" class="pagination-next">Older &rarr;</a>
-    {{end}}
-  </nav>
-  {{end}}
-</div>
-{{end}}