Initial commit: Xiaoxiang Smart BMS Home Assistant integration

- BLE GATT communication via bleak (UART-over-GATT, service 0xff00)
- Parses 0x03 (general info) and 0x04 (cell voltages) frames
- Protocol verified against official RS485/UART spec V4
- DataUpdateCoordinator with 5s poll interval (configurable 2-60s)
- Auto-reconnect on BLE disconnect
- Config flow: BT auto-discovery + manual MAC entry + options flow
- Sensors: voltage, current, power, SoC, capacity, cycles, temps, cells, cell delta
- HACS-ready (hacs.json, manifest.json)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

custom_components/xiaoxiang_bms/strings.json

@@ -0,0 +1,40 @@
+{
+  "config": {
+    "step": {
+      "user": {
+        "title": "Xiaoxiang Smart BMS",
+        "description": "Enter the Bluetooth address of your BMS, or select a discovered device from the dropdown.",
+        "data": {
+          "address": "Bluetooth Address"
+        },
+        "data_description": {
+          "address": "MAC address of the BMS (e.g. AA:BB:CC:DD:EE:FF). Tip: pair the device first via your system Bluetooth settings."
+        }
+      },
+      "confirm": {
+        "title": "Confirm Xiaoxiang BMS",
+        "description": "Connect to **{name}** ({address})?\n\nMake sure the BMS is powered on and within Bluetooth range."
+      }
+    },
+    "abort": {
+      "already_configured": "This BMS is already configured."
+    },
+    "error": {
+      "cannot_connect": "Unable to connect to the BMS. Check the address and try again."
+    }
+  },
+  "options": {
+    "step": {
+      "init": {
+        "title": "BMS Options",
+        "description": "Adjust the polling interval. Lower values give more accurate real-time readings but use more Bluetooth bandwidth.",
+        "data": {
+          "poll_interval": "Poll interval (seconds)"
+        },
+        "data_description": {
+          "poll_interval": "How often to request data from the BMS (2–60 seconds). Default is 5 s for solar/energy monitoring."
+        }
+      }
+    }
+  }
+}