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/Features/Settings/SettingsScreen.swift

@@ -93,7 +93,9 @@ struct SettingsScreen: View {
 		// Contacts brings its own Form and push destination, so it is not wrapped
 		// in the shared section chrome.
 		if section == .contacts {
-			ContactsScreen(model: contacts)
+			ContactsScreen(model: contacts) {
+				model.reportNothingWaiting()
+			}
 		} else {
 			settingsSectionForm(section)
 		}