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

collect.py

@@ -296,7 +296,16 @@ def collect(config: dict, dry_run: bool = False) -> list[str]:
             if not src.is_dir():
                 errors.append(f"{name}: {kind} site missing ({src})")
                 continue
-            dst = ROOT / name
+            if site_rel == "site":
+                # Kinds share a single site root; copy only the per-kind
+                # subdir so stray root output never leaks into the hub.
+                src = src / kind
+                if not src.is_dir():
+                    errors.append(f"{name}: {kind} site subdir missing ({src})")
+                    continue
+                dst = ROOT / name / kind
+            else:
+                dst = ROOT / name
             copied.append(f"{kind:>4}  {name}  {dst.relative_to(ROOT)}/")
             if not dry_run:
                 _copy_dir(src, dst)