feat: Add state persistence for cover entities

Implements RestoreEntity to maintain cover position and state after Home Assistant restarts.

Changes:
- Add RestoreEntity mixin to AirSendCover class
- Implement async_added_to_hass() to restore previous state
- Position restoration for type 4099 covers (with position support)
- Open/closed state restoration for all cover types
- Maintains backward compatibility with 50% default for new covers

Fixes issue where covers would reset to 50% position after every restart.

custom_components/airsend/cover.py

@@ -6,6 +6,7 @@ from .device import Device
 from homeassistant.components.cover import CoverEntity
 from homeassistant.core import HomeAssistant
 from homeassistant.helpers.typing import ConfigType
+from homeassistant.helpers.restore_state import RestoreEntity
 from homeassistant.const import CONF_DEVICES, CONF_INTERNAL_URL
 
 from . import DOMAIN
@@ -26,7 +27,7 @@ async def async_setup_platform(
             async_add_entities([entity])
 
 
-class AirSendCover(CoverEntity):
+class AirSendCover(CoverEntity, RestoreEntity):
     """Representation of an AirSend Cover."""
 
     def __init__(
@@ -43,6 +44,33 @@ class AirSendCover(CoverEntity):
         if device.is_cover_with_position:
             self._attr_current_cover_position = 50
 
+    async def async_added_to_hass(self):
+        """Restore last known state when added to hass."""
+        await super().async_added_to_hass()
+        
+        # Get the last known state
+        last_state = await self.async_get_last_state()
+        
+        if last_state:
+            # Restore position for covers with position support (type 4099)
+            if self._device.is_cover_with_position:
+                # Try to restore position from attributes
+                if last_state.attributes.get('current_position') is not None:
+                    self._attr_current_cover_position = last_state.attributes['current_position']
+                
+                # Override position based on state if fully open/closed
+                if last_state.state == 'closed':
+                    self._attr_current_cover_position = 0
+                elif last_state.state == 'open':
+                    self._attr_current_cover_position = 100
+            
+            # Restore closed/open state for all covers
+            if last_state.state == 'closed':
+                self._closed = True
+            elif last_state.state == 'open':
+                self._closed = False
+        # If no last_state, keep the defaults (50% for position covers)
+
     @property
     def unique_id(self):
         """Return unique identifier of remote device."""