[VISHNU0906]

#335 fixed this for get_entities_related_to_a_file; the other five related-entities tools still have it.

get_entities_related_to_a_domain, _an_ip_address, _an_url, _a_collection and _a_hunting_ruleset return {"error": "Relationship X does not exist. Available relationships are: ..."} for an unknown relationship_name, but they are annotated as returning a list. FastMCP validates the return value against that output schema, so the client gets this instead of the error dict:

ToolError: Error executing tool get_entities_related_to_a_domain: 1 validation error for get_entities_related_to_a_domainOutput
result
  Input should be a valid list [type=list_type, ...]

That hides the list of valid relationships, which is what the model needs to retry. This PR gives the five tools the same Union[List[Dict], Dict[str, str]] return annotation the file tool has now and notes the error dict in their docstrings.

Testing: a new parametrized test calls each tool through the MCP client session with an unknown relationship and checks the error dict comes back; all five cases fail on main with the validation error above. The full server/gti suite passes (72 tests).

@dandye could you take a look when you have a moment?

[dandye]

Thanks for catching the remaining five tools and adding the parametrized client-session regression test. LGTM, merging now.