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/magazine/+page.svelte

@@ -27,7 +27,7 @@
         const matchesSearch =
           article.title.toLowerCase().includes(searchQuery.toLowerCase()) ||
           article.excerpt?.toLowerCase().includes(searchQuery.toLowerCase()) ||
-          article.author?.first_name?.toLowerCase().includes(searchQuery.toLowerCase());
+          article.author?.artist_name?.toLowerCase().includes(searchQuery.toLowerCase());
         const matchesCategory = categoryFilter === "all" || article.category === categoryFilter;
         return matchesSearch && matchesCategory;
       })
@@ -190,11 +190,11 @@
               <div class="flex items-center gap-3">
                 <img
                   src={getAssetUrl(featuredArticle.author?.avatar, "mini")}
-                  alt={featuredArticle.author?.first_name}
+                  alt={featuredArticle.author?.artist_name}
                   class="w-10 h-10 rounded-full object-cover"
                 />
                 <div>
-                  <p class="font-medium">{featuredArticle.author?.first_name}</p>
+                  <p class="font-medium">{featuredArticle.author?.artist_name}</p>
                   <div class="flex items-center gap-3 text-sm text-muted-foreground">
                     <span>{timeAgo.format(new Date(featuredArticle.publish_date))}</span>
                     <span>•</span>
@@ -288,11 +288,11 @@
               <div class="flex items-center gap-2">
                 <img
                   src={getAssetUrl(article.author?.avatar, "mini")}
-                  alt={article.author?.first_name}
+                  alt={article.author?.artist_name}
                   class="w-8 h-8 rounded-full object-cover"
                 />
                 <div>
-                  <p class="text-sm font-medium">{article.author?.first_name}</p>
+                  <p class="text-sm font-medium">{article.author?.artist_name}</p>
                   <div class="flex items-center gap-2 text-xs text-muted-foreground">
                     <span class="icon-[ri--calendar-line] w-4 h-4"></span>
                     {timeAgo.format(new Date(article.publish_date))}