fix: sync reactive state with data prop using \$effect

Replaces bare \$state(data.x) initialisers (which only capture the
initial value) with \$state + \$effect pairs so that state stays in sync
whenever page data is invalidated or the URL changes. Affects all list
pages (searchValue) and all edit/detail pages (form fields).

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

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

@@ -29,6 +29,20 @@
   let selectedModelIds = $state<string[]>(
     data.video.models?.map((m: { id: string }) => m.id) ?? [],
   );
+  $effect(() => {
+    title = data.video.title;
+    slug = data.video.slug;
+    description = data.video.description ?? "";
+    tags = data.video.tags ?? [];
+    premium = data.video.premium ?? false;
+    featured = data.video.featured ?? false;
+    uploadDate = data.video.upload_date
+      ? new Date(data.video.upload_date).toISOString().slice(0, 16)
+      : "";
+    imageId = data.video.image ?? null;
+    movieId = data.video.movie ?? null;
+    selectedModelIds = data.video.models?.map((m: { id: string }) => m.id) ?? [];
+  });
   let saving = $state(false);
 
   async function handleImageUpload(files: File[]) {