Fix application crash on WiFi page

src/wifi_setup_page.h

@@ -37,6 +37,7 @@ private:
     AppState* state_ = nullptr;
     InputMode inputMode_ = InputMode::Normal;
     int selectedIndex_ = 0;
+    std::string selectedSsid_ = "";
 
     std::string passwordInput_ = "";
     std::string statusMessage_ = "Press F5 to scan for available networks";