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>

.claude/settings.local.json

@@ -0,0 +1,9 @@
+{
+  "permissions": {
+    "allow": [
+      "WebFetch(domain:raw.githubusercontent.com)",
+      "WebSearch",
+      "WebFetch(domain:api.github.com)"
+    ]
+  }
+}