Fix context not being stored as member variable

The setContext() method was setting prefs but not storing context as a class member variable, causing generateDeviceIdentity() to always see null context.

app/src/main/java/com/nexlab/openclaw/node/data/remote/NodeClient.kt

@@ -71,8 +71,10 @@ class NodeClient() {
 
     // SharedPreferences for device identity persistence
     private var prefs: SharedPreferences? = null
+    private var context: Context? = null
     
     fun setContext(context: Context) {
+        this.context = context
         prefs = context.getSharedPreferences("openclaw_device_identity", Context.MODE_PRIVATE)
         // Regenerate identity if needed (will load existing if available)
         generateDeviceIdentity()