fix: log exception when openclaw.json token read fails for easier debugging

Agent-Logs-Url: https://github.com/mithun50/openclaw-termux/sessions/2f5ef8ee-b8bf-4ee1-ab15-ba2a1603670c

Co-authored-by: mithun50 <99024517+mithun50@users.noreply.github.com>

Author: Copilot

flutter_app/lib/services/node_service.dart

@@ -171,7 +171,9 @@ class NodeService {
           return token;
         }
       }
-    } catch (_) {}
+    } catch (e) {
+      _log('[NODE] Could not read token from openclaw.json: $e');
+    }
 
     _log('[NODE] No gateway token available');
     return null;