feat(doctor): device prereqs replace java/sidecar for ios-device

iosDeviceChecks now verifies devicectl, iproxy on PATH, a connected+paired
device (via ios.ConnectedDevices), and App Store Connect signing creds (via
ioscompanion.VerifyDeviceSigning). The retired JVM sidecar checks stay only
under android.

internal/driver/ioscompanion/devicerunner.go

@@ -75,6 +75,14 @@ func readSigningCredentials() (signingCredentials, error) {
 	return creds, nil
 }
 
+// VerifyDeviceSigning reports whether the device signing environment is complete
+// and the App Store Connect key file exists. The doctor calls it so the device
+// preflight surfaces missing credentials before a run reaches the build step.
+func VerifyDeviceSigning() error {
+	_, err := readSigningCredentials()
+	return err
+}
+
 func firstNonEmpty(values ...string) string {
 	for _, value := range values {
 		if value != "" {

internal/ios/device.go

@@ -39,6 +39,12 @@ type coreDeviceList struct {
 // canned devicectl output without invoking xcrun.
 var listDevices = coreDevices
 
+// ConnectedDevices lists the physical iOS devices devicectl reports. The doctor
+// uses it to confirm at least one device is connected and paired.
+func ConnectedDevices(ctx context.Context) ([]Device, error) {
+	return listDevices(ctx)
+}
+
 // ResolveDevice picks the physical iOS device a run drives. An empty query
 // resolves the single connected device (an error names them all when several
 // are connected). A non-empty query matches a device by name, hardware UDID, or