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/frontend/src/routes/admin/users/[id]/+page.svelte

@@ -21,6 +21,7 @@
   let artistName = $state(data.user.artist_name ?? "");
   let avatarId = $state<string | null>(data.user.avatar ?? null);
   let bannerId = $state<string | null>(data.user.banner ?? null);
+  let photoId = $state<string | null>(data.user.photo ?? null);
   let isAdmin = $state(data.user.is_admin ?? false);
   let saving = $state(false);
 
@@ -52,6 +53,20 @@
     }
   }
 
+  async function handlePhotoUpload2(files: File[]) {
+    const file = files[0];
+    if (!file) return;
+    const fd = new FormData();
+    fd.append("file", file);
+    try {
+      const res = await uploadFile(fd);
+      photoId = res.id;
+      toast.success($_("admin.user_edit.model_photo_uploaded"));
+    } catch {
+      toast.error($_("admin.user_edit.model_photo_failed"));
+    }
+  }
+
   async function handlePhotoUpload(files: File[]) {
     for (const file of files) {
       const fd = new FormData();
@@ -88,6 +103,7 @@
         artistName: artistName || undefined,
         avatarId: avatarId || undefined,
         bannerId: bannerId || undefined,
+        photoId: photoId || undefined,
         isAdmin,
       });
       toast.success($_("admin.user_edit.save_success"));
@@ -158,6 +174,20 @@
       <FileDropZone accept="image/*" maxFileSize={10 * MEGABYTE} onUpload={handleBannerUpload} />
     </div>
 
+    <!-- Model photo (used in cards & model page, not for avatar/comments) -->
+    <div class="space-y-1.5">
+      <Label>{$_("admin.user_edit.model_photo")}</Label>
+      <p class="text-xs text-muted-foreground">{$_("admin.user_edit.model_photo_hint")}</p>
+      {#if photoId}
+        <img
+          src={getAssetUrl(photoId, "preview")}
+          alt=""
+          class="w-full h-48 rounded object-cover mb-2"
+        />
+      {/if}
+      <FileDropZone accept="image/*" maxFileSize={10 * MEGABYTE} onUpload={handlePhotoUpload2} />
+    </div>
+
     <!-- Admin flag -->
     <label
       class="flex items-center gap-3 rounded-lg border border-border/40 px-4 py-3 cursor-pointer hover:bg-muted/20 transition-colors"