fix: treat empty string as no filter in mempalace_search wing/room (MemPalace#1097)

* fix: treat empty string as no filter in mempalace_search wing/room

* fix: also treat whitespace-only strings as no filter

Author: KunalG67

mempalace/mcp_server.py

@@ -285,7 +285,7 @@ def _get_cached_metadata(col, where=None):
 
 def _sanitize_optional_name(value: str = None, field_name: str = "name") -> str:
     """Validate optional wing/room-style filters."""
-    if value is None:
+    if value is None or not value.strip():
         return None
     return sanitize_name(value, field_name)