docs(create_task): add quantity convention to text parameter (v0.5.2)

Documents the preferred format for quantities in shopping list tasks:
item name first, quantity in parentheses at the end.
Examples: "Äpfel (5x)", "Hackfleisch (500g)", "Joghurt (Erdbeere, 2x)".

No functional code changes.

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

src/mcp_familywall/server.py

@@ -693,6 +693,9 @@ def create_task(
     Args:
         list_id: Target list ID from get_lists (e.g. ``taskList/123_456``).
         text: Task title / main text.
+            For quantities use the format "Äpfel (5x)" — item name first,
+            quantity in parentheses at the end. Examples:
+            "Äpfel (5x)", "Hackfleisch (500g)", "Joghurt (Erdbeere, 2x)".
         description: Optional longer description.
         category_id: Optional category metaId from get_categories
             (e.g. ``taskCategory/23431854_200``). Only meaningful for