fix: wrap raw list returns in response models to produce single TextContent block

MCP tools returning raw lists caused FastMCP's _convert_to_content() to create
one TextContent block per element. Most MCP clients only read content[0], so
they saw a single result instead of the full list.

Wrapped 9 tool functions in proper response objects:
- deck: deck_get_boards, deck_get_stacks, deck_get_cards, deck_get_labels
- calendar: nc_calendar_list_events, nc_calendar_get_upcoming_events
- contacts: nc_contacts_list_addressbooks, nc_contacts_list_contacts
- tables: nc_tables_list_tables

Closes #568

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nextcloud_mcp_server/models/deck.py

@@ -261,6 +261,20 @@ class CreateLabelResponse(BaseResponse):
     color: str = Field(description="The created label color")
 
 
+class ListCardsResponse(BaseResponse):
+    """Response model for listing deck cards."""
+
+    cards: List[DeckCard] = Field(description="List of deck cards")
+    total: int = Field(description="Total number of cards")
+
+
+class ListLabelsResponse(BaseResponse):
+    """Response model for listing deck labels."""
+
+    labels: List[DeckLabel] = Field(description="List of deck labels")
+    total: int = Field(description="Total number of labels")
+
+
 class LabelOperationResponse(StatusResponse):
     """Response model for label operations like update/delete."""