feat: add ValidateDeviceToken method to device auth middleware

Add device token validation method for WebSocket authentication:
- Validates device auth tokens against database
- Returns device information for valid tokens
- Used by WebSocket handler for device authentication

This enables devices to authenticate WebSocket connections
using their bearer tokens.

internal/middleware/device_auth.go

@@ -2,6 +2,7 @@ package middleware
 
 import (
 	"bookmann/internal/database"
+	"context"
 	"net/http"
 	"strings"
 
@@ -173,3 +174,7 @@ func (m *DeviceAuthMiddleware) UpdateLastSeen(next echo.HandlerFunc) echo.Handle
 		return err
 	}
 }
+
+func (m *DeviceAuthMiddleware) ValidateDeviceToken(token string) (database.Devices, error) {
+	return m.db.GetDeviceByAuthToken(context.Background(), token)
+}