fix: correct XIAO RS485 UART pin mapping

tests/test_dashboard_source_contract.py

@@ -44,6 +44,8 @@ def test_dashboard_receives_sensor_node_rs485_for_diagnostics():
     assert 'strcmp(type, "sensor_status")' in receiver
     assert 'doc["frame_sequence"]' in receiver
     assert "framesDropped" in receiver
+    assert "bytesReceived++" in receiver
+    assert r'text += "\n  Raw bytes/age: "' in dashboard
     assert 'imu["yaw_degrees"]' in receiver
     assert 'gps["altitude_meters"]' in receiver
     assert 'JsonObject utc = gps["utc"]' in receiver

tests/test_xiao_sensor_node_contract.py

@@ -7,7 +7,7 @@ def source(name): return (NODE / name).read_text()
 
 def test_wiring_matches_assembly():
     config = source("sensor_node_config.h")
-    expected = {"RS485_DE_PIN":"D2", "RS485_TX_PIN":"D4", "RS485_RX_PIN":"D5",
+    expected = {"RS485_DE_PIN":"D2", "RS485_RX_PIN":"D4", "RS485_TX_PIN":"D5",
                 "BNO086_SDA_PIN":"D7", "BNO086_SCL_PIN":"D8", "GPS_RX_PIN":"D9", "GPS_TX_PIN":"D10"}
     for name, pin in expected.items(): assert re.search(rf"#define\s+{name}\s+{pin}\b", config)