fix(frontend): Svelte 5 reactivity, each block keys, and path resolution

Add proper keys to #each blocks across 15+ components to fix reordering bugs. Replace new Date() with SvelteDate in reactive contexts. Use $derived for computed values (totalPages). Use resolve() from $app/paths for all internal navigation hrefs. Add ARIA labels and keyboard accessibility to NavBar mobile menu. Remove unused handleRetry from UserPaymentModal.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

frontend/src/lib/components/admin/TimeBlockers.svelte

@@ -735,7 +735,7 @@
 						/>
 					</div>
 					<div class="space-y-2">
-						<label class="text-xs text-gray-600">Time</label>
+						<div class="text-xs text-gray-600">Time</div>
 						{#if hoursLoading}
 							<Skeleton class="h-9 w-full" />
 						{:else if !selectedWorkingHours}
@@ -912,7 +912,7 @@
 </Modal.Root>
 
 <AlertDialog.Root bind:open={showDeleteAlert}>
-	<AlertDialog.Content class="z-[60]">
+	<AlertDialog.Content class="z-60">
 		<AlertDialog.Header>
 			<AlertDialog.Title>Delete time blocker?</AlertDialog.Title>
 			<AlertDialog.Description>