Fix loading state stuck when API calls fail on startup

Add try/catch to all onMount API calls so the UI recovers
gracefully when the server isn't ready yet instead of hanging
on the loading skeleton forever.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/src/routes/+page.svelte

@@ -10,7 +10,9 @@
   let selectedGroup = $state('');
 
   onMount(async () => {
+    try {
       [categories, groups] = await Promise.all([getCategories(), getGroups()]);
+    } catch { /* server may not be ready yet */ }
   });
 
   function handleSearch(e) {

src/client/src/routes/admin/+page.svelte

@@ -7,8 +7,13 @@
   let syncMessage = $state('');
 
   onMount(async () => {
+    try {
       stores = await getStores();
+    } catch (err) {
+      console.error('Failed to load stores:', err);
+    } finally {
       loading = false;
+    }
   });
 
   async function handleToggle(id) {

src/client/src/routes/admin/categories/+page.svelte

@@ -16,8 +16,13 @@
   let editingCat = $state(null);
 
   onMount(async () => {
+    try {
       [categories, groups, stores] = await Promise.all([getCategories(), getGroups(), getStores()]);
+    } catch (err) {
+      console.error('Failed to load data:', err);
+    } finally {
       loading = false;
+    }
   });
 
   async function handleAddCategory() {