feat: add dedicated model photo separate from avatar

Adds a `photo` field to the users table (and a migration) that serves
as a dedicated profile/card image for models. This is now used in model
cards and on the model single page, while `avatar` is reserved for
comments, article authors, and the user profile page.

- DB: `photo` column on `users` with FK to `files`
- GraphQL: exposed on ModelType, UserType, AdminUserDetailType; photoId arg on adminUpdateUser
- Services: photo field in MODELS_QUERY, MODEL_BY_SLUG_QUERY, ADMIN_GET/UPDATE_USER
- Frontend: model cards and single page use `photo ?? avatar` fallback
- Admin: model photo upload section in user edit page

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/types/src/index.ts

@@ -27,6 +27,8 @@ export interface User {
   avatar: string | null;
   /** UUID of the banner file */
   banner: string | null;
+  /** UUID of the dedicated model profile/card image */
+  photo: string | null;
   email_verified: boolean;
   date_created: Date;
 }
@@ -81,6 +83,8 @@ export interface Model {
   description: string | null;
   avatar: string | null;
   banner: string | null;
+  /** UUID of the dedicated model profile/card image (distinct from avatar) */
+  photo: string | null;
   tags: string[] | null;
   date_created: Date;
   photos?: ModelPhoto[];