fix(tests): uuid-suffixed websocket collection self-deletes

TestWebSocketUserScopedBroadcast creates "Admin Collection <uuid8>" on
the shared admin — deliberately NOT named with "test" or every run
would 409 on UNIQUE(user_id, name) against stranded past-run rows
(the comment in the test says exactly that), but it never deleted its
row, so the same runs accrued ten "Admin Collection" forever-rows the
name sweep can never touch. cleanupCollectionByID gives tests an
owner-scoped RLS-bridge delete-at-backstory: same minimal contract as
cleanupDeviceByIdentifier, for rows whose name must stay unique across
runs. Deleted the ten standing rows (owner-scoped, exactly what the
cleanup path does).

What CANNOT be swept, audited safe: the dev admin's real hand-made
collections (Saga reading-orders, Podcast 2, Smart Collection (Books))
carry no sweepable names; devices rely on identifier/token prefixes
tests own exclusively; the rls-phone hand account persists because the
transient-user sweep matches only @tests.bookhoard.internal /
@example.com emails.

cmd/server/tests/websocket_test.go

@@ -241,6 +241,10 @@ func TestWebSocketUserScopedBroadcast(t *testing.T) {
 	err = json.NewDecoder(collectionResp.Body).Decode(&collectionResult)
 	require.NoError(t, err)
 	collectionID := collectionResult["id"].(string)
+	// The uuid suffix keeps the name off every run's UNIQUE(user_id,name),
+	// which also keeps it out of the name-based cleanup sweep — self-delete
+	// instead (owner-scoped, exactly who created it).
+	cleanupCollectionByID(t, setup, getTestUserID(t, setup.DB), collectionID)
 
 	// Create a test book via API
 	bookID := createTestMediaItemID(t, setup)