Each of Newbook, Resos, SambaPOS, SMTP, and Nextcloud now has a checkbox at the
top of its credentials block. When enabled, the app reads auth credentials from
the central stack settings service (SETTINGS_URL + STACK_INTERNAL_SECRET) and
the local auth fields are grayed out. App-specific fields (base path, GL codes,
keywords, sync intervals, etc.) remain editable regardless.
Backend: new use_global_* columns on kitchen_settings, migration, global_settings_service
with apply_global_overrides() for in-memory credential injection, GET /api/settings/global-status
endpoint, and apply_global_overrides() called in test-connection endpoints and FileArchivalService.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
