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

config.yml

@@ -132,13 +132,6 @@ static:
       lib: yes
       wiki: yes
 
-  - kind: api
-    repo: blog
-    title: Blog API
-    description: A modular, async Blog API backend for FastAPI microservices. Provides streamlined CRUD operations for articles and authors.
-    section: apps
-    path: blog
-
   - kind: tutorial
     repo: media-manager
     title: Media Manager Tutorial