feat(deck): surface remapped labels in move-card response

Round-3 review polish on PR #885:

- deck_move_card_to_board now captures the moved DeckCard and returns its
  post-move label titles in CardOperationResponse.labels, so LLM clients can
  confirm the cross-board label remap (the tool's headline behaviour) without
  a follow-up deck_get_card. The field is optional and defaults to None for
  the other card operations that share this response model.
- Tighten test_move_card_to_board_restores_done_state to assert the returned
  card reflects the restored done state.

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

nextcloud_mcp_server/models/deck.py

@@ -337,6 +337,14 @@ class CardOperationResponse(StatusResponse):
     card_id: int = Field(description="ID of the affected card")
     stack_id: int = Field(description="ID of the stack containing the card")
     board_id: int = Field(description="ID of the board containing the card")
+    labels: list[str] | None = Field(
+        default=None,
+        description=(
+            "Label titles on the card after the operation, when relevant — "
+            "e.g. after a cross-board move that remaps board-scoped labels to "
+            "the destination board"
+        ),
+    )
 
 
 # Label Response Models