Fix multiple inverters creating duplicate device instead of separate devices

PROBLEM:
When users added a second inverter (different IP address), it recreated
the same device as the first inverter instead of creating a second device
in Home Assistant. Both inverters' entities appeared under one device.

ROOT CAUSE:
Device identifier in coordinator.py used slave_id:
  "identifiers": {(DOMAIN, self._slave_id)}

Both inverters typically use slave_id=1 (default), so Home Assistant
considered them the same device and merged all entities into one.

FIX:
Changed device identifier to use config entry_id (coordinator.py:536):
  "identifiers": {(DOMAIN, self.entry.entry_id)}

Config entry_id is unique per integration instance, guaranteed to be
different for each inverter added, even if they have the same slave_id.

RESULT:
Users can now add multiple inverters (at different IP addresses) and
each will appear as a separate device with its own sensors.

MIGRATION NOTE:
Existing users will see their device re-created with a new ID after
updating. The old device may need to be manually removed from:
Settings → Devices & Services → Devices (search for old Growatt device)

Author: claude

custom_components/growatt_modbus/coordinator.py

@@ -527,25 +527,26 @@ def _parse_model_name(self, inverter_type: str, profile: dict) -> str:
     def device_info(self):
         """Return device information for Home Assistant."""
         profile = REGISTER_MAPS[self._register_map_key]
-        
+
         # Use parsed model name if available, otherwise fall back to profile name
         model = self._model_name if self._model_name else profile.get("name", "Unknown Model")
-        
+
         device_info = {
-            "identifiers": {(DOMAIN, self._slave_id)},
+            # Use entry_id for unique device identification (not slave_id, which may be the same for multiple inverters)
+            "identifiers": {(DOMAIN, self.entry.entry_id)},
             "name": self.config[CONF_NAME],
             "manufacturer": "Growatt",
             "model": model,
         }
-        
+
         # Add serial number if available
         if self._serial_number:
             device_info["serial_number"] = self._serial_number
-        
+
         # Add firmware version if available
         if self._firmware_version:
             device_info["sw_version"] = self._firmware_version
-        
+
         return device_info
 
     @property