make_graphql_request now reads credentials from the settings module at call
time (via a local import) instead of relying on module-level names captured at
import time. When either credential is missing it raises CredentialsNotConfiguredError
(not ToolError), allowing callers to trigger elicitation rather than surfacing a
generic error to the MCP client.
Updated tests/test_client.py and tests/http_layer/test_request_construction.py
to patch unraid_mcp.config.settings.* instead of the now-removed client-module
attrs, and to expect CredentialsNotConfiguredError on missing credentials.
