When an LLM generates a valid JSON string that parses to a native non-dict
type (like a list, int, or string), _parse_tool_args previously returned
that object. Callers expecting a dictionary would then crash with
AttributeError or KeyError when attempting to look up action keys.
- Update _parse_tool_args in src/tool_utils.py to explicitly type-check
the parsed JSON object and return {} for non-dict objects.
- Add test coverage in tests/test_admin_tools_registry.py for lists,
ints, and strings.
