firmware: scaffold optional cargo OLED display

tests/test_http_api_contract.py

@@ -401,3 +401,27 @@ def test_embedded_webui_config_subtabs():
     assert "config-maintenance" in source
     assert "WiFi / AP" in source
     assert "subtabbtn active" in source
+
+
+def test_cargo_oled_support_is_optional():
+    source = firmware_source()
+
+    assert "#define OLED_ENABLED 0" in source
+    assert "#if OLED_ENABLED" in source
+    assert "void oledBegin()" in source
+    assert "void oledLoop()" in source
+    assert "void oledShowSetupPage()" in source
+    assert "OLED_I2C_ADDR = 0x3C" in source
+    assert "Adafruit_SSD1306" in source
+
+
+def test_cargo_oled_shows_setup_and_service_pages():
+    source = firmware_source()
+
+    assert 'oledClear("Setup / AP")' in source
+    assert 'oledClear("Battery")' in source
+    assert 'oledClear("Relays")' in source
+    assert 'oledClear("Network")' in source
+    assert 'oledClear("Alarms")' in source
+    assert "oledShowSetupPage();" in source
+    assert "oledLoop();" in source