Kiosk: System Name entry in System Settings

Adds a System Name text-entry page (hint 'e.g. Living Room', 1-40 char
validation) and a data-driven System Settings row for it. Saving persists
locally and nudges the background sync; conflict/invalid results surface
the message and restore the previous name. Extends the settings-menu
tests.

src/system_settings_page.cpp

@@ -6,6 +6,7 @@
 #include "logical_size.h"
 #include "timezone_page.h"
 #include "wifi_setup_page.h"
+#include "system_name_page.h"
 #include <SDL3/SDL.h>
 #include <SDL3_image/SDL_image.h>
 #include <algorithm>
@@ -76,6 +77,9 @@ void SystemSettingsPage::activateSelected(AppState &state)
     case radiantwave::settings::SystemSettingId::LicenseKey:
         state.pages.push(state, std::make_unique<LicenseKeyPage>());
         break;
+    case radiantwave::settings::SystemSettingId::SystemName:
+        state.pages.push(state, std::make_unique<SystemNamePage>());
+        break;
     case radiantwave::settings::SystemSettingId::WiFiSetup:
         state.pages.push(state, std::make_unique<WiFiSetupPage>());
         break;