fix(housekeeping): exclude files that are used as app icons or avatar images from being removed (#20532)

api/commands.py

         {"type": "text", "table": "workflow_node_executions", "column": "outputs"},
         {"type": "text", "table": "conversations", "column": "introduction"},
         {"type": "text", "table": "conversations", "column": "system_instruction"},
+        {"type": "text", "table": "accounts", "column": "avatar"},
+        {"type": "text", "table": "apps", "column": "icon"},
+        {"type": "text", "table": "sites", "column": "icon"},
         {"type": "json", "table": "messages", "column": "inputs"},
         {"type": "json", "table": "messages", "column": "message"},
     ]