docs(deck): note owner reassignment on move; add archived-preservation test

Round-2 review polish on PR #885:

- Document in the deck_move_card_to_board tool that the move reassigns the
  card owner to the calling user and resets the done timestamp (both are
  limitations of Deck's move route), so an LLM reading only the tool
  description isn't misled about preserved fields.
- Fix the done integration-test docstring to say "done state (not timestamp)".
- Add test_move_card_to_board_preserves_archived_status to lock in the
  documented archived-preservation behaviour.

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

nextcloud_mcp_server/server/deck.py

@@ -1268,11 +1268,16 @@ def configure_deck_tools(mcp: FastMCP):
     ) -> CardOperationResponse:
         """Move a Nextcloud Deck card to a stack on a different board.
 
-        The card keeps its identity (same id, comments, attachments). Deck
-        remaps the card's board-scoped labels to the destination board by
-        title — reusing a same-titled label there, or cloning it when you have
-        board-manage permission. Use deck_reorder_card for moves within a
-        single board.
+        The card keeps its identity (same id, comments, attachments), along
+        with its archived state and due date. Deck remaps the card's
+        board-scoped labels to the destination board by title — reusing a
+        same-titled label there, or cloning it when you have board-manage
+        permission. Use deck_reorder_card for moves within a single board.
+
+        Two caveats from Deck's move route: the card's owner is reassigned to
+        the user performing the move (the original owner is not preserved), and
+        a card marked done keeps its done state but its done timestamp is reset
+        to the time of the move.
 
         target_stack_id must be a stack on target_board_id; the move is
         rejected otherwise.