feat(apple): contacts screen and consent prompts

Device list, detail, and block list under Settings, plus the two sheets:
an incoming offer and a device asking to be remembered. Both are
answer-only, since swiping away would leave the sender waiting.

Accepting an offer routes the released ticket into the ordinary receive
path, so the platform still chooses the destination. The prompt does not
ask a second time; it only falls back to the review sheet when the
destination is unusable.

apple/VniDrop/Features/Contacts/ContactPrompts.swift

@@ -0,0 +1,133 @@
+import SFSafeSymbols
+import SwiftUI
+
+/// Consent prompts for device history, presented as sheets like the receiver
+/// approval modal.
+///
+/// Both are dismissable by answering only. An incoming offer in particular must
+/// not be acceptable by accident, and a swipe-away would leave the sender
+/// waiting on a decision that never comes.
+struct ContactPromptHost: View {
+	/// Driven by the host so a prompt is never presented while another sheet is
+	/// still animating out — macOS silently drops the second one.
+	@Binding var isPresented: Bool
+	let state: ContactsState
+	let onPairingResponse: (String, Bool) -> Void
+	let onOfferResponse: (String, Bool) -> Void
+
+	var body: some View {
+		Color.clear
+			.sheet(isPresented: $isPresented) {
+				// An incoming transfer is the more urgent of the two, and a
+				// pairing offer keeps until the consent window lapses.
+				if let offer = state.currentOffer {
+					OfferSheet(
+						offer: offer,
+						busy: state.busyOfferIds.contains(offer.offerId),
+						onRespond: onOfferResponse
+					)
+					.interactiveDismissDisabled(true)
+					.modifier(ContactPromptDetents())
+				} else if let pairing = state.currentPairing {
+					PairingSheet(
+						pairing: pairing,
+						busy: state.busyEndpoints.contains(pairing.endpointId),
+						onRespond: onPairingResponse
+					)
+					.interactiveDismissDisabled(true)
+					.modifier(ContactPromptDetents())
+				}
+			}
+	}
+}
+
+private struct ContactPromptDetents: ViewModifier {
+	func body(content: Content) -> some View {
+		#if os(iOS)
+		content.presentationDetents([.medium])
+		#else
+		content.frame(minWidth: 420, minHeight: 300)
+		#endif
+	}
+}
+
+/// "A remembered device wants to send you files."
+private struct OfferSheet: View {
+	let offer: IncomingOfferModel
+	let busy: Bool
+	let onRespond: (String, Bool) -> Void
+
+	var body: some View {
+		VStack(spacing: 16) {
+			Image(systemSymbol: .trayAndArrowDownFill)
+				.font(.system(size: 44))
+				.foregroundStyle(.tint)
+				.padding(.top, 12)
+			Text(String(localized: L10n.Offer.title))
+				.font(.title2).fontWeight(.semibold)
+			Text(L10n.Offer.body(device: offer.resolvedSenderName, transferName: offer.transferName))
+				.multilineTextAlignment(.center)
+			Text(L10n.Transfer.fileCount(count: Int(offer.fileCount)))
+				.font(.caption)
+				.foregroundStyle(.secondary)
+			Spacer(minLength: 0)
+			HStack(spacing: 12) {
+				Button(role: .cancel) {
+					onRespond(offer.offerId, false)
+				} label: {
+					Text(String(localized: L10n.Offer.decline)).frame(maxWidth: .infinity)
+				}
+				Button {
+					onRespond(offer.offerId, true)
+				} label: {
+					Text(String(localized: L10n.Offer.accept)).frame(maxWidth: .infinity)
+				}
+				.buttonStyle(.borderedProminent)
+			}
+			.disabled(busy)
+		}
+		.padding(20)
+	}
+}
+
+/// "This device offered to let you reach it. Remember it?"
+private struct PairingSheet: View {
+	let pairing: PendingPairingModel
+	let busy: Bool
+	let onRespond: (String, Bool) -> Void
+
+	var body: some View {
+		VStack(spacing: 16) {
+			Image(systemSymbol: .laptopcomputerAndIphone)
+				.font(.system(size: 44))
+				.foregroundStyle(.tint)
+				.padding(.top, 12)
+			Text(String(localized: L10n.Pairing.requestTitle))
+				.font(.title2).fontWeight(.semibold)
+			Text(L10n.Pairing.requestBody(device: pairing.resolvedName))
+				.multilineTextAlignment(.center)
+			// Names are peer-supplied; the endpoint id is what actually identifies
+			// the device.
+			Text(L10n.Approval.endpointId(deviceId: pairing.endpointId))
+				.font(.caption)
+				.foregroundStyle(.secondary)
+				.multilineTextAlignment(.center)
+			Spacer(minLength: 0)
+			HStack(spacing: 12) {
+				Button(role: .cancel) {
+					onRespond(pairing.endpointId, false)
+				} label: {
+					Text(String(localized: L10n.Pairing.decline)).frame(maxWidth: .infinity)
+				}
+				Button {
+					onRespond(pairing.endpointId, true)
+				} label: {
+					Text(String(localized: L10n.Pairing.accept)).frame(maxWidth: .infinity)
+				}
+				.buttonStyle(.borderedProminent)
+			}
+			.disabled(busy)
+		}
+		.padding(20)
+	}
+}