fix: add str() cast in fetch_entity_category for mypy

categories.get(scope) returns Any from untyped dict; cast to
str to match declared str | None return type.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kingpanther13

src/ha_mcp/tools/util_helpers.py

@@ -388,7 +388,8 @@ async def fetch_entity_category(
         )
         if result.get("success"):
             categories = result.get("result", {}).get("categories", {})
-            return categories.get(scope)
+            cat_id = categories.get(scope)
+            return str(cat_id) if cat_id is not None else None
     except Exception as e:
         logger.debug(f"Failed to fetch category for {entity_id}: {e}")
     return None