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/server/deck.py

@@ -1291,7 +1291,7 @@ def configure_deck_tools(mcp: FastMCP):
             order: Position within the destination stack (default 0 = top)
         """
         client = await get_client(ctx)
-        await client.deck.move_card_to_board(
+        moved = await client.deck.move_card_to_board(
             source_board_id,
             source_stack_id,
             card_id,
@@ -1299,12 +1299,15 @@ def configure_deck_tools(mcp: FastMCP):
             target_stack_id,
             order,
         )
+        # Surface the post-move labels so callers can confirm the remap without
+        # a follow-up get_card (label remapping is this tool's whole point).
         return CardOperationResponse(
             success=True,
             message="Card moved to board successfully",
             card_id=card_id,
             stack_id=target_stack_id,
             board_id=target_board_id,
+            labels=[label.title for label in (moved.labels or [])],
         )
 
     # Label Tools