feat(apple): collect transfers held for this device

Adds the opt-in foreground check and an explicit Check now, the waiting-to-
be-delivered list on the sender side, and honest reporting when a send could
not be delivered: a closed app is a delay, not a success nobody received.

The setting is off by default and its footer states that checking reveals
app-open times to remembered devices, since that is the reason it is a
setting at all.

Records in the design doc that this shipped as one global toggle rather than
the per-contact opt-in originally specified.

apple/VniDrop/Core/CoreRepository.swift

@@ -335,7 +335,7 @@ final class CoreRepository: ObservableObject, CoreGateway {
 		sources: [ShareSource],
 		transferName: String,
 		senderName: String
-	) async -> Result<Share, Error> {
+	) async -> Result<ContactSendOutcome, Error> {
 		guard !isNetworkTransitionInProgress else {
 			return .failure(CoreNetworkLifecycleError.transitionInProgress)
 		}
@@ -355,10 +355,18 @@ final class CoreRepository: ObservableObject, CoreGateway {
 					accessMode: .approvalRequired
 				)
 			)
-			return result.toModel()
+			return ContactSendOutcome(share: result.share.toModel(), delivered: result.delivered)
 		}
 	}
 
+	func heldOffers() async -> Result<[HeldOfferModel], Error> {
+		await runCore { try self.requireCore().listHeldOffers().map { $0.toModel() } }
+	}
+
+	func pollContactsForOffers() async -> Result<UInt64, Error> {
+		await runCore { try self.requireCore().pollContactsForOffers() }
+	}
+
 	func forgetContact(endpointId: String) async -> Result<Void, Error> {
 		await runCore { try self.requireCore().forgetContact(endpointId: endpointId) }
 	}
@@ -657,6 +665,20 @@ extension IncomingOffer {
 	}
 }
 
+extension HeldOfferSummary {
+	func toModel() -> HeldOfferModel {
+		HeldOfferModel(
+			offerId: offerId,
+			endpointId: endpointId,
+			transferId: transferId,
+			transferName: transferName,
+			fileCount: fileCount,
+			totalBytes: totalBytes,
+			createdAt: createdAt
+		)
+	}
+}
+
 extension GrantLifetimeOption {
 	func toNative() -> GrantLifetimeSetting {
 		switch self {