style: standardise select styling in DiscountsManagement, HolidayHours, TodayCalendar

Update select element classes to consistent h-9, shadow-xs, bg-background, focus-visible ring styling.

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

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

frontend/src/lib/components/today/TodayCalendar.svelte

@@ -935,7 +935,7 @@
 					<p class="text-sm text-red-500">Closed today</p>
 				{:else}
 					<select
-						class="flex h-9 w-full rounded-md border border-input bg-transparent px-3 text-sm"
+						class="flex h-9 w-full rounded-md border border-input bg-background px-3 py-1 text-sm shadow-xs ring-offset-background transition-[color,box-shadow] outline-none focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50"
 						bind:value={startSelectValue}
 						onchange={() => {
 							const p = parseSelectValue(startSelectValue);
@@ -963,7 +963,7 @@
 					<p class="text-sm text-gray-400">No available end time after selected start</p>
 				{:else}
 					<select
-						class="flex h-9 w-full rounded-md border border-input bg-transparent px-3 text-sm"
+						class="flex h-9 w-full rounded-md border border-input bg-background px-3 py-1 text-sm shadow-xs ring-offset-background transition-[color,box-shadow] outline-none focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50"
 						bind:value={endSelectValue}
 						onchange={() => {
 							const p = parseSelectValue(endSelectValue);