refactor: align article author with VideoModel, streamline selects, fix flyout inert

- Remove ArticleAuthor type; article.author now reuses VideoModel (id, artist_name, slug, avatar)
- updateArticle accepts authorId; author selectable in admin article edit page
- Article edit: single Select with bind:value + $derived selectedAuthor display
- Video edit: replace pill toggles with Select type="multiple" bind:value for models
- Video table: replace inline badge spans with Badge component
- Magazine: display artist_name throughout, author bio links to model profile
- Fix flyout aria-hidden warning: replace with inert attribute

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

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

@@ -10,6 +10,7 @@
   import { TagsInput } from "$lib/components/ui/tags-input";
   import { FileDropZone, MEGABYTE } from "$lib/components/ui/file-drop-zone";
   import { getAssetUrl } from "$lib/api";
+  import { Select, SelectContent, SelectItem, SelectTrigger } from "$lib/components/ui/select";
 
   const { data } = $props();
 
@@ -24,6 +25,8 @@
     data.article.publish_date ? new Date(data.article.publish_date).toISOString().slice(0, 16) : "",
   );
   let imageId = $state<string | null>(data.article.image ?? null);
+  let authorId = $state(data.article.author?.id ?? "");
+  let selectedAuthor = $derived(data.authors.find((a) => a.id === authorId) ?? null);
   let saving = $state(false);
   let editorTab = $state<"write" | "preview">("write");
 
@@ -53,6 +56,7 @@
         excerpt: excerpt || undefined,
         content: content || undefined,
         imageId: imageId || undefined,
+        authorId: authorId || null,
         tags,
         category: category || undefined,
         featured,
@@ -139,6 +143,34 @@
       <FileDropZone accept="image/*" maxFileSize={10 * MEGABYTE} onUpload={handleImageUpload} />
     </div>
 
+    <!-- Author -->
+    <div class="space-y-1.5">
+      <Label>Author</Label>
+      <Select type="single" bind:value={authorId}>
+        <SelectTrigger class="w-full">
+          {#if selectedAuthor}
+            {#if selectedAuthor.avatar}
+              <img src={getAssetUrl(selectedAuthor.avatar, "mini")} alt="" class="h-5 w-5 rounded-full object-cover shrink-0" />
+            {/if}
+            {selectedAuthor.artist_name}
+          {:else}
+            <span class="text-muted-foreground">No author</span>
+          {/if}
+        </SelectTrigger>
+        <SelectContent>
+          <SelectItem value="">No author</SelectItem>
+          {#each data.authors as author (author.id)}
+            <SelectItem value={author.id}>
+              {#if author.avatar}
+                <img src={getAssetUrl(author.avatar, "mini")} alt="" class="h-5 w-5 rounded-full object-cover shrink-0" />
+              {/if}
+              {author.artist_name}
+            </SelectItem>
+          {/each}
+        </SelectContent>
+      </Select>
+    </div>
+
     <div class="grid grid-cols-1 sm:grid-cols-2 gap-4">
       <div class="space-y-1.5">
         <Label for="category">Category</Label>