Show captive portal status and sign-in action in network panel

test/shell.d/fixtures/network-captive-portal/mocks/NetworkMock.qml

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+pragma Singleton
+import QtQuick
+import Quickshell.Networking
+
+QtObject {
+  property int backend: NetworkBackendType.NetworkManager
+  property bool wifiEnabled: true
+  property bool canCheckConnectivity: true
+  property bool connectivityCheckEnabled: true
+  property int connectivity: NetworkConnectivity.Full
+  property int checks: 0
+  function checkConnectivity() { checks++ }
+
+  property var devices: ({ values: [wifi] })
+  property QtObject wifi: QtObject {
+    property int type: DeviceType.Wifi
+    property string name: "test-wifi"
+    property bool connected: true
+    property bool scannerEnabled: false
+    property var networks: ({ values: [network] })
+  }
+  property QtObject network: QtObject {
+    property string name: "Guest Wi-Fi"
+    property bool connected: true
+    property bool known: true
+    property bool stateChanging: false
+    property real signalStrength: 0.8
+    property int security: WifiSecurityType.Open
+    signal connectionFailed(int reason)
+  }
+}

test/shell.d/fixtures/network-captive-portal/mocks/qmldir

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+singleton NetworkMock 1.0 NetworkMock.qml