Add one-time setup links as an alternative to the QR code

A config can now be handed over as a one-time link, valid for 1 h, 24 h or
7 days and protected by a PIN by default. Keys are made only when the link
is opened; the link works once and is revoked after 5 wrong PINs. Issuing a
new config offers the same choice, and the current config keeps working
until the link is used.

Remove the option to paste a client's public key, in the web UI, the API
and the iOS app.

ios/GHOSTWIRE/Models.swift

@@ -112,9 +112,18 @@ nonisolated struct Peer: Decodable, Identifiable, Hashable {
     let effectiveKeepalive: Int
     let created: Date
     let configIssued: Date?
+    let setup: SetupInfo?       // pending setup link, nil if none
     let stats: PeerStats
 }
 
+/// A pending setup link as peer lists show it. The link itself is not in it.
+nonisolated struct SetupInfo: Decodable, Hashable {
+    let expires: Date
+    let expired: Bool
+    let pinRequired: Bool
+    let pinFails: Int
+}
+
 nonisolated struct PeerList: Decodable {
     let peers: [Peer]
     let capacity: Int