fix: process weather art images correctly

- Add processing for webp_image and preview_image

This fix ensures that both webp and preview images of the weather art
are processed correctly after generation, resolving issues related to
image availability in the system.

app/workers/generate_weather_art_worker.rb

@@ -53,6 +53,8 @@ class GenerateWeatherArtWorker
         filename: generate_filename,
         content_type: "image/png"
       )
+      weather_art.webp_image.processed
+      weather_art.preview_image.processed
 
       weather_art
     end