test(deck): address PR #872 round-2 review

- Assert the open card stays visible under status="open" in the
  deck_get_stack integration test (completes the partition check).
- Move the _append_archived_cards docstring closing quotes to their own line.

deck_get_stack's status="archived" + include_cards=False path is left as-is:
a single get_stack call is the cheapest way to obtain the stack metadata
there — routing it through the archived fast-path would fetch every archived
stack on the board just to strip the cards, which is heavier, not lighter.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/server/deck.py

@@ -242,7 +242,8 @@ def _append_archived_cards(stack: DeckStack, extra: list[DeckCard]) -> None:
     """Append archived cards onto a stack's existing card list, in place.
 
     Kept separate so the assignment stays correctly typed against
-    ``DeckStack.cards`` (``list[DeckCard | DeckCardSummary] | None``)."""
+    ``DeckStack.cards`` (``list[DeckCard | DeckCardSummary] | None``).
+    """
     merged: list[DeckCard | DeckCardSummary] = list(stack.cards or [])
     merged.extend(extra)
     stack.cards = merged