fix(roaming): 权限授予后页面内刷新状态

问题：用户在页面内跳系统设置授予定位权限再回来，GPS 监听不启动（必须退出重进页面）。
根因：permissionLauncher 回调是空的 { }，不更新 hasPermission 状态。
修复：回调里检查 FINE/COARSE 权限并更新 hasPermission，触发 DisposableEffect 启动 GPS 监听。
影响：用户授权后立即生效，无需退出重进。

feature/roaming/src/main/java/com/rtbishop/look4sat/feature/roaming/RoamingScreen.kt

@@ -89,7 +89,11 @@ fun RoamingScreen() {
     var hasPermission by remember { mutableStateOf(false) }
     val permissionLauncher = rememberLauncherForActivityResult(
         ActivityResultContracts.RequestMultiplePermissions()
-    ) { }
+    ) { results ->
+        val fine = results[Manifest.permission.ACCESS_FINE_LOCATION] == true
+        val coarse = results[Manifest.permission.ACCESS_COARSE_LOCATION] == true
+        hasPermission = fine || coarse
+    }
     LaunchedEffect(Unit) {
         hourPrefix = SimpleDateFormat("HH:mm", Locale.getDefault()).format(Date()).substring(0, 3)
         val fine = ContextCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION) ==