test: the gate's output carries no noise to hide a real warning in

- Home tests mocked the api without downloadIndex, so every card's download button logged a
  missing-queryFn error (64 stderr blocks per run).
- QueryState rendered without an i18n instance; Modal.fullscreen awaited a synchronous act,
  which React reports as an act environment it does not support.
- pytest: Starlette 1.x's TestClient is built on httpx2 and warned on every run without it
  (pinned in requirements-dev); alembic.ini declares its path separator.

backend/alembic.ini

@@ -1,6 +1,8 @@
 [alembic]
 script_location = alembic
 prepend_sys_path = .
+# Split the path list the way the OS does (alembic's legacy space/comma/colon split is deprecated).
+path_separator = os
 
 [loggers]
 keys = root,sqlalchemy,alembic