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/videos/[slug]/+page.svelte

@@ -30,6 +30,10 @@
   const timeAgo = new TimeAgo("en");
   let isLiked = $state(data.likeStatus.liked);
   let likesCount = $state(data.video.likes_count || 0);
+  $effect(() => {
+    isLiked = data.likeStatus.liked;
+    likesCount = data.video.likes_count || 0;
+  });
   let isLikeLoading = $state(false);
   let newComment = $state("");
   let showComments = $state(true);