fix: theme store stuck on loading skeleton after fetch failures

Harden theme list fetching with normalized API responses, timeouts, retries,
and a visible error state so the store no longer stays blank when messaging
or payloads fail (common after extension updates without a SEQTA tab reload).

src/interface/components/store/CoverSwiper.svelte

@@ -10,14 +10,18 @@
   }>();
   let emblaApi = $state();
 
-  const options = { loop: true };
-  const plugins = [
-    Autoplay({
-      delay: 5000,
-      stopOnInteraction: false,
-      stopOnMouseEnter: true,
-    }),
-  ];
+  const options = $derived({ loop: slides.length > 1 });
+  const plugins = $derived(
+    slides.length > 1
+      ? [
+          Autoplay({
+            delay: 5000,
+            stopOnInteraction: false,
+            stopOnMouseEnter: true,
+          }),
+        ]
+      : [],
+  );
 
   function onInit(event: CustomEvent) {
     emblaApi = event.detail;

src/interface/components/store/ThemeGrid.svelte

@@ -21,9 +21,12 @@
     allStoreThemeRows?: Theme[];
   }>();
   
-  let filteredThemes = $derived(themes.filter((theme: Theme) =>
-    theme.name.toLowerCase().includes(searchTerm.toLowerCase()) || theme.description.toLowerCase().includes(searchTerm.toLowerCase())
-  ));
+  let filteredThemes = $derived(themes.filter((theme: Theme) => {
+    const q = searchTerm.toLowerCase();
+    const name = (theme.name ?? '').toLowerCase();
+    const description = (theme.description ?? '').toLowerCase();
+    return name.includes(q) || description.includes(q);
+  }));
 </script>
 
 <div class="relative" >

src/interface/components/store/ThemeModal.svelte

@@ -234,7 +234,7 @@
 
   $effect(() => {
 
-    if (displayTheme) {
+    if (displayTheme && modalElement) {
 
       animate(