style: refine admin edit forms and fix mobile padding

- Remove back button from admin entity edit pages (sidebar handles navigation)
- Remove cancel button from video/article forms, make submit button full-width
- Show actual entity title + subtitle on video/article edit pages
- Remove asterisks from Title/Slug field labels in i18n
- Remove px-3 sm:px-0 from all admin list page headers/filters (fixes mobile padding)

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

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

@@ -98,11 +98,11 @@
 <Meta title={$_("admin.article_form.edit_title")} description={null} />
 
 <div class="py-3 sm:py-6 lg:pl-6">
-  <div class="flex items-center gap-4 mb-6">
-    <Button variant="ghost" href="/admin/articles" size="sm" class="shrink-0">
-      <span class="icon-[ri--arrow-left-line] h-4 w-4 mr-1"></span>{$_("common.back")}
-    </Button>
-    <h1 class="text-2xl font-bold">{$_("admin.article_form.edit_title")}</h1>
+  <div class="mb-6">
+    <h1 class="text-2xl font-bold">{data.article.title}</h1>
+    <p class="text-xs text-muted-foreground mt-0.5">
+      {data.article.slug}{data.article.category ? " · " + data.article.category : ""}{data.article.author ? " · " + data.article.author.artist_name : ""}
+    </p>
   </div>
 
   <Card class="bg-card/50 border-primary/20 max-w-4xl">
@@ -246,16 +246,13 @@
         <span class="text-sm">{$_("admin.common.featured")}</span>
       </label>
 
-      <div class="flex gap-3 pt-2">
-        <Button
-          onclick={handleSubmit}
-          disabled={saving}
-          class="cursor-pointer bg-gradient-to-r from-primary to-accent hover:from-primary/90 hover:to-accent/90"
-        >
-          {saving ? $_("admin.common.saving") : $_("admin.common.save_changes")}
-        </Button>
-        <Button variant="outline" href="/admin/articles">{$_("common.cancel")}</Button>
-      </div>
+      <Button
+        onclick={handleSubmit}
+        disabled={saving}
+        class="cursor-pointer w-full bg-gradient-to-r from-primary to-accent hover:from-primary/90 hover:to-accent/90"
+      >
+        {saving ? $_("admin.common.saving") : $_("admin.common.save_changes")}
+      </Button>
     </CardContent>
   </Card>
 </div>