Connecting was one-way: POST could only replace the base URL, and the only
escape was hand-editing settings.json. DELETE now mirrors POST — drop the
stored section, delete the reserved key, unregister the provider from
piModels() — and the connect editor grows a Disconnect beside Connect,
following the stored-key rows' Delete pattern (quiet text, one click, no
confirm, only once there is an endpoint to remove).
Review pass: shorten verbose doc comments across the custom-endpoint code,
merge duplicate imports, share one synthetic provider entry between the keys
section and setup dialog, collapse the duplicated connect-editor block, revert
an unrelated settings-route drive-by.
Daniel Buckner