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/WalkInCreateModal.svelte

@@ -152,7 +152,7 @@
 				return;
 			}
 
-			const now = new Date();
+			const now = new SvelteDate();
 			const diff = reservationExpiresAt.getTime() - now.getTime();
 
 			if (diff <= 0) {
@@ -545,9 +545,9 @@
 							<div class="max-h-[300px] overflow-y-auto rounded-md border border-gray-200">
 								{#if loadingUsers}
 									<div class="space-y-2 p-2">
-										{#each Array(3) as _}
-											<Skeleton class="h-10 w-full" />
-										{/each}
+									{#each Array(3) as _, i (i)}
+										<Skeleton class="h-10 w-full" />
+									{/each}
 									</div>
 								{:else if users.length === 0}
 									<div class="flex items-center justify-center p-8 text-sm text-gray-500">
@@ -653,7 +653,7 @@
 					<Card.Content class="space-y-4">
 						{#if loadingServices}
 							<div class="grid grid-cols-1 gap-4 md:grid-cols-2">
-								{#each Array(4) as _}
+								{#each Array(4) as _, i (i)}
 									<Skeleton class="h-28 w-full" />
 								{/each}
 							</div>