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/videos/+page.svelte

@@ -4,6 +4,7 @@
   import { deleteVideo } from "$lib/services";
   import { getAssetUrl } from "$lib/api";
   import { Button } from "$lib/components/ui/button";
+  import { Badge } from "$lib/components/ui/badge";
   import * as Dialog from "$lib/components/ui/dialog";
   import type { Video } from "$lib/types";
 
@@ -81,15 +82,10 @@
             <td class="px-4 py-3 hidden sm:table-cell">
               <div class="flex gap-1">
                 {#if video.premium}
-                  <span
-                    class="px-1.5 py-0.5 rounded text-xs font-medium bg-yellow-500/10 text-yellow-600"
-                    >Premium</span
-                  >
+                  <Badge variant="outline" class="text-yellow-600 border-yellow-500/40 bg-yellow-500/10">Premium</Badge>
                 {/if}
                 {#if video.featured}
-                  <span class="px-1.5 py-0.5 rounded text-xs font-medium bg-primary/10 text-primary"
-                    >Featured</span
-                  >
+                  <Badge variant="default">Featured</Badge>
                 {/if}
               </div>
             </td>