Scene Manager: request publishes missing on this site

- Request (globe) on casting rows and loaded assets whose latest publish
  is not on this site, and Request Missing for all of them, through the
  new wtdcmds command wtd_request_revisions. Requested publishes show
  "requested, waiting for the download".
- The version picker requests a version that is not on this site.
- A 404 explains that the session is gone or wtdcmds is too old.
- Fake server: car (vehicles) with a publish not on this site,
  wtd_request_revisions and /_test/download; 45 checks.
- Tested live: car_paul modeling.blend v001 -> Requested.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dev/make_test_assets.py

@@ -4,6 +4,7 @@
 
 bob: a rig (COL_bob: armature + meshes), v001 has 1 mesh, v002 has 2.
 tree: COL_tree, plus an unrelated top-level collection.
+car: COL_car.
 rock: a single top-level collection not named after the asset (fallback case), its mesh
 using a node group linked from Blender's essentials (an indirect library).
 """
@@ -56,4 +57,5 @@ write(os.path.join(lib, "bob", "v001", "rig.blend"), "COL_bob", meshes=1, rig=Tr
 write(os.path.join(lib, "bob", "v002", "rig.blend"), "COL_bob", meshes=2, rig=True, extra=True)
 write(os.path.join(lib, "tree", "v001", "model.blend"), "COL_tree", extra=True)
 write(os.path.join(lib, "rock", "v001", "rock.blend"), "rock_geo", node_group=True)
+write(os.path.join(lib, "car", "v001", "car.blend"), "COL_car")
 print("Test assets written in", lib)