Add an edit affordance to each saved server in ServerConnectScreen: a
pencil button loads the entry into the form (Edit Server mode) with
Save Changes / Cancel actions. Persisted via a new
ServerPreferences.updateSavedServer() that replaces by connection
identity (address/port/scheme) and keeps the active record in sync when
the edited server is the active one.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>