Backend (CRM expert): Custom field definitions CRUD, bulk value upsert,
7 endpoints, Prisma schema with CustomFieldDef + CustomFieldValue tables.
Frontend: Types, API, hooks, admin settings page with field management,
CustomFieldsDisplay for detail pages, CustomFieldsForm for edit modals.
Also fix Vite allowedHosts for insight.xinion.lan.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>