navi_ui is navi's own MCP server (navi/mcp/ui_server), started in-process on
NAVI_UI_MCP_PORT — 8098. The config still carried the pre-8099/8098 default,
localhost:8001, where nothing has listened for a long time: on prod the connect
fails on every start and render_component only ever appeared as an unregistered
phantom in list_tools.

The URL now names the loopback literal rather than "localhost", which can
resolve to ::1 while the server binds IPv4 only.

Three tests assert the file against the live FastMCP object (host, port, path,
transport) instead of a second copy of the setting — with the old URL two of
them fail, so the drift that produced this cannot come back unnoticed.