Add software brightness control for Adalight devices

Emulates hardware brightness by multiplying pixel values before serial
send. Stored per-device and persisted across restarts.

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

server/src/wled_controller/storage/device_store.py

@@ -33,6 +33,7 @@ class Device:
         enabled: bool = True,
         device_type: str = "wled",
         baud_rate: Optional[int] = None,
+        software_brightness: int = 255,
         calibration: Optional[CalibrationConfig] = None,
         created_at: Optional[datetime] = None,
         updated_at: Optional[datetime] = None,
@@ -44,6 +45,7 @@ class Device:
         self.enabled = enabled
         self.device_type = device_type
         self.baud_rate = baud_rate
+        self.software_brightness = software_brightness
         self.calibration = calibration or create_default_calibration(led_count)
         self.created_at = created_at or datetime.utcnow()
         self.updated_at = updated_at or datetime.utcnow()
@@ -63,6 +65,8 @@ class Device:
         }
         if self.baud_rate is not None:
             d["baud_rate"] = self.baud_rate
+        if self.software_brightness != 255:
+            d["software_brightness"] = self.software_brightness
         return d
 
     @classmethod
@@ -87,6 +91,7 @@ class Device:
             enabled=data.get("enabled", True),
             device_type=data.get("device_type", "wled"),
             baud_rate=data.get("baud_rate"),
+            software_brightness=data.get("software_brightness", 255),
             calibration=calibration,
             created_at=datetime.fromisoformat(data.get("created_at", datetime.utcnow().isoformat())),
             updated_at=datetime.fromisoformat(data.get("updated_at", datetime.utcnow().isoformat())),