Introduce initial UI for connecting to networks

Apple/App/TunnelButton.swift

@@ -0,0 +1,61 @@
+import SwiftUI
+
+struct TunnelButton: View {
+    @Environment(\.tunnel)
+    var tunnel: any Tunnel
+
+    var body: some View {
+        if let action = tunnel.action {
+            Button {
+                tunnel.perform(action)
+            } label: {
+                Text(action.description)
+            }
+            .padding(.horizontal)
+            .buttonStyle(.floating)
+        }
+    }
+}
+
+extension Tunnel {
+    fileprivate var action: TunnelButton.Action? {
+        switch status {
+        case .permissionRequired, .invalid:
+            .enable
+        case .disabled, .disconnecting, .disconnected:
+            .start
+        case .connecting, .connected, .reasserting:
+            .stop
+        case .unknown, .configurationReadWriteFailed:
+            nil
+        }
+    }
+}
+
+extension TunnelButton {
+    fileprivate enum Action {
+        case enable
+        case start
+        case stop
+    }
+}
+
+extension TunnelButton.Action {
+    var description: LocalizedStringKey {
+        switch self {
+        case .enable: "Enable"
+        case .start: "Start"
+        case .stop: "Stop"
+        }
+    }
+}
+
+extension Tunnel {
+    fileprivate func perform(_ action: TunnelButton.Action) {
+        switch action {
+        case .enable: enable()
+        case .start: start()
+        case .stop: stop()
+        }
+    }
+}