Add a "Disable auto mode server check" quick toggle to the Claude
provider editor that writes CLAUDE_CODE_AUTO_MODE_SERVER=0, with a hint
explaining that third-party gateways cannot serve the check and that
official endpoints should leave it unchecked.
New Claude providers now get the key by default unless the preset is
official or a cloud provider, or the preset already sets it. The default
form (no live base yet) also goes through the overlay so the custom
provider starts with the same value.
