fix: Tier-2 involved mediums — send confirm re-validation + console JSON errors

- Send: re-validate against LIVE state at the "Confirm & Send" click (connected,
  not syncing, amount > 0, total <= available). The confirm dialog persists
  across frames, so a balance drop / sync restart / fee bump after Review could
  otherwise broadcast a now-invalid transaction; it now shows a clear message
  instead of sending.
- Console: a malformed JSON argument ({...}/[...] that fails to parse) was
  silently sent to the daemon as a plain string. Now the command fails with a
  clear "Argument N is not valid JSON" line instead of being silently mangled.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/windows/console_command_executor.cpp

@@ -48,7 +48,13 @@ void FullNodeConsoleExecutor::submit(const std::string& cmd)
     }
 
     auto call = BuildConsoleRpcCall(cmd);
-    if (!call.valid) return;
+    if (!call.valid) {
+        if (!call.error.empty()) {
+            std::lock_guard<std::mutex> lk(results_mutex_);
+            results_.push_back({call.error, true});
+        }
+        return;
+    }
     const std::string method = call.method;
     const nlohmann::json params = call.params;