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

hexa/mcp/nav.json

@@ -1,38 +0,0 @@
-[
-  {
-    "module": "hexa",
-    "resource": "doc://modules/hexa"
-  },
-  {
-    "module": "hexa.check_matches",
-    "resource": "doc://modules/hexa.check_matches"
-  },
-  {
-    "module": "hexa.cli",
-    "resource": "doc://modules/hexa.cli"
-  },
-  {
-    "module": "hexa.container",
-    "resource": "doc://modules/hexa.container"
-  },
-  {
-    "module": "hexa.generate_abc",
-    "resource": "doc://modules/hexa.generate_abc"
-  },
-  {
-    "module": "hexa.generate_yaml",
-    "resource": "doc://modules/hexa.generate_yaml"
-  },
-  {
-    "module": "hexa.model",
-    "resource": "doc://modules/hexa.model"
-  },
-  {
-    "module": "hexa.parse_abc",
-    "resource": "doc://modules/hexa.parse_abc"
-  },
-  {
-    "module": "hexa.parse_yaml",
-    "resource": "doc://modules/hexa.parse_yaml"
-  }
-]