feat(frontend): add deposit and payment warnings to cancel modal

Shows the total amount already paid in the cancellation confirmation, plus deposit-specific messaging: forfeiture warning when deposit is paid, and a note that outstanding deposit is no longer due when deposit is required but not yet paid.

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

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

frontend/src/lib/components/account/UserBookingModal.svelte

@@ -634,16 +634,35 @@
 		<Modal.Header>
 			<Modal.Title>Cancel Booking</Modal.Title>
 			<Modal.Description>
-				Are you sure you want to cancel this booking?
+				{#if hasPayments}
+					<p>
+						Are you sure you want to cancel this booking? You have already made payments totalling
+						<span class="font-semibold">£{totalPaid.toFixed(2)}</span>.
+					</p>
+				{:else}
+					Are you sure you want to cancel this booking?
+				{/if}
 				{#if hasPayments}
 					<div
 						class="mt-2 rounded-md border border-amber-200 bg-amber-50 p-3 text-sm text-amber-800"
 					>
 						<p class="font-medium">Please note:</p>
 						<p class="mt-1">
-							The <span class="font-semibold">£{totalPaid.toFixed(2)}</span> already paid for this booking
-							will not be refunded, but will be retained as credit towards a future appointment.
+							Any amounts paid (<span class="font-semibold">£{totalPaid.toFixed(2)}</span>) will
+							not be refunded, but will be retained as credit towards a future appointment.
 						</p>
+						{#if selectedBooking}
+							{#if selectedBooking.deposit_paid}
+								<p class="mt-1">
+									The deposit of
+									<span class="font-semibold">£{selectedBooking.deposit_amount?.toFixed(2)}</span>
+									paid for this booking may be forfeited.
+								</p>
+							{/if}
+							{#if selectedBooking.deposit_required && !selectedBooking.deposit_paid}
+								<p class="mt-1">Any outstanding deposit will no longer be due.</p>
+							{/if}
+						{/if}
 					</div>
 				{/if}
 			</Modal.Description>