fix: vendor per-kind sites in the hub; drop stale blog docs

- collect.py: when a kind points at the shared site root, copy only the
  per-kind subdir (site/lib -> <repo>/lib) instead of the whole site, so
  stray single-site build output never leaks into the hub
- Purge stale collected artifacts (404.html, assets/, search/, sitemaps,
  objects.inv, duplicate mcp/) from every repo dir, matching the cleaned
  source site/ roots
- Refresh collected output from source repos, incl. the khata-app app
- Remove the vendored Blog API docs (config.yml entry + blog/) and its card

_index/index.html

@@ -105,13 +105,6 @@
       <a href="/khata-app/lib/" target="_blank">view lib</a>
     </div>
   </div>
-  <div class="card">
-    <h3>Blog API</h3>
-    <p>A modular, async Blog API backend for FastAPI microservices. Provides streamlined CRUD operations for articles and authors.</p>
-    <div class="card-actions">
-      <a href="/blog/" target="_blank">view docs</a>
-    </div>
-  </div>
 </div>
 </section>