DeleteWithPathPrefix queried the share index with the raw path, so deleting a
directory through a trailing-slash path (e.g. DELETE /api/resources/a/) only
matched descendants like /a/child and missed the exact /a share, leaving it in
storage. If the same path was later recreated, the stale public share re-exposed
the new content. Normalize the path before the prefix query so the exact share
and its descendants are both removed. Adds a regression test.
