Add Rexense integration doc

source/_integrations/rexense.markdown

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+---
+title: Rexense
+description: "Integrate Rexense IoT Mesh devices"
+ha_category:
+  - Sensor
+  - Switch
+ha_release: 2025.04
+ha_codeowners:
+  - '@rexense'
+ha_iot_class: local_push
+ha_domain: rexense
+featured: false
+ha_config_flow: true
+ha_zeroconf: true
+ha_platforms:
+  - sensor
+  - switch
+ha_integration_type: device
+---
+
+Integrate [Rexense IoT Mesh devices](https://www.rexense.com) into Home Assistant.
+
+## High-level description
+The Rexense integration enables Home Assistant to automatically discover and manage Rexense IoT Mesh devices, providing automated device discovery, real‑time sensor data, and switch control.
+
+## Installation instructions
+1. **Enable default integrations**
+   In your `configuration.yaml`, add:
+   ```yaml
+   default_config:
+   zeroconf:
+   ```
+2. **Restart Home Assistant**
+3. **Add Rexense**
+   - Go to **Settings → Devices & Services**
+   - Click **Add integration**
+   - Search for **Rexense** and select it
+   - Follow the prompts to either auto-discover your devices or enter **Host** and **Port** manually
+
+Once configured, HA will fetch `/rex/GetBasicInfo` over HTTP then upgrade to a WebSocket at `/rpc` for live updates.
+
+## Configuration options
+
+{% include integrations/config_flow.md %}
+
+## WebSocket push updates
+After initial HTTP setup, the integration upgrades the connection to WebSocket for live updates. Sensor values and switch states are pushed in real time, and Home Assistant entities update immediately.
+
+## Entities
+
+### Sensors
+For `REX-3PHASEMETER-01` models, the following sensors are created:
+- **Phase A/B/C:** Current, Voltage, Active Power, Apparent Power, Power Factor
+- **Totals:** Total Active Power, Total Apparent Power, Cumulative Energy Imported/Exported
+- **Temperature**
+
+Each sensor has:
+- **Unique ID:** `<device_id>_<sensor_type>`
+- **Device & state class** for correct presentation
+- **Automatic name** generated from device model and sensor type
+
+## Removal instructions
+
+{% include integrations/remove_device_service.md %}
+