fix(tools): handle non-dict JSON values in _parse_tool_args (closes #5043) (#5064)

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.

src/tool_utils.py

@@ -54,6 +54,8 @@ def _parse_tool_args(content):
     if isinstance(content, str):
         try:
             args = json.loads(content) if content.strip() else {}
+            if not isinstance(args, dict):
+                args = {}
         except (json.JSONDecodeError, TypeError) as e:
             raise ValueError(str(e))
     elif isinstance(content, dict):