Config object starts empty so the frontend had nothing to render for
plaintext fields (region, username etc). Now populates all schema-defined
fields with empty string when not yet saved.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Fastify API for storing third-party integration credentials (Newbook, Resos,
Nextcloud, Azure, SambaPOS) with AES-256-GCM encryption for sensitive fields.
Includes Newbook room sync endpoint and global_config store for shared app data.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
