feat: add scheduled change UI and conflict display to weekly schedule

Convert WeeklySchedule to schedule staged changes with an effective date picker and conflict detection UI. Show pending scheduled changes in BusinessHours component. Update admin page to pass through props.

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

@@ -126,7 +126,8 @@
 				]);
 
 				if (hoursRes.ok) {
-					defaultHours = await hoursRes.json();
+					const result = await hoursRes.json();
+					defaultHours = result.current || [];
 				}
 				if (servicesRes.ok) {
 					services = await servicesRes.json();
@@ -379,7 +380,7 @@
 				<div class="space-y-4 p-4">
 					<TimeBlockers {openUserModal} {openBookingModal} {rescheduleVersion} {defaultHours} />
 					<HolidayHours {openUserModal} {openBookingModal} {rescheduleVersion} />
-					<WeeklySchedule {defaultHours} />
+					<WeeklySchedule {defaultHours} {openUserModal} {openBookingModal} {rescheduleVersion} />
 				</div>
 			{/if}
 		</div>