DOC-8: say EMS port, not meter bus

The add-on is wired to the inverter's RS485 port labelled EMS. Reword
README, DOCS, config description, field guide source and HTML. The HA
manufacturer string is left unchanged: test_mqtt pins it byte for byte.

Co-Authored-By: Claude <noreply@anthropic.com>

goodwe_controller/DOCS.md

@@ -1,7 +1,7 @@
 # GoodWe RS485 Controller
 
-Drives a GoodWe ES/BP battery inverter over its RS485 meter bus: holds net grid
-exchange at zero, and runs a monthly battery maintenance cycle so the BMS can
+Drives a GoodWe ES/BP battery inverter over its RS485 EMS port: sends it a grid
+reading to hold net grid exchange at zero, and runs a monthly battery maintenance cycle so the BMS can
 balance cells and recalibrate its coulomb counter.
 
 Installers: the printed field guide (`docs/GoodWe-RS485-Field-Guide.pdf`) is
@@ -33,8 +33,8 @@ v0.1.0 and outdated; where it disagrees with this page, this page wins.
 
 You need:
 
-- A GoodWe **ES / BP family** inverter (AA55 / RS485 meter-bus generation)
-- The vendor's meter-emulating controller **disconnected** from the bus
+- A GoodWe **ES / BP family** inverter (AA55 generation)
+- The vendor's controller **disconnected** from the inverter's EMS port
 - A control board: a T-CAN485 (ESP32) flashed with
   `firmware/goodwe-master.yaml`
 - A grid-power sensor already working in Home Assistant, updating every ~5–10 s