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/app/main.py

@@ -3,7 +3,7 @@
 WHAT THIS THING DOES, in one paragraph: it reads the house's net grid power from
 Home Assistant, decides how hard the battery should charge or discharge to hold
 that at zero, and writes that figure to an ESP32 which puts it on the inverter's
-RS485 meter bus. Once a month it runs a full low->full battery cycle so the BMS
+RS485 EMS port. Once a month it runs a full low->full battery cycle so the BMS
 can balance cells and recalibrate its coulomb counter.
 
 ⚠️ THE ONE THING TO UNDERSTAND BEFORE CHANGING ANY OF THIS: the inverter holds