Add JPG support for online_image in lvgl

**Describe the problem you have/What new integration you would like**

Currently online_image only supports PNG format it would be amazing if this could be extended to JPG to avoid having to convert images on-the-fly at source

**Please describe your use case for this integration and alternatives you've tried:**

I'm attempting to build a Spotify player on a Guition ESP32-S3-4848S040 480*480 Smart Screen (https://devices.esphome.io/devices/Guition-ESP32-S3-4848S040), unfortunately the HA Spotify media_player outputs the entity_image in a JPG format.

I've attempted to use imagemagick on the host HA system to convert the JPG to a resized PNG, with varying degrees of success, but ultimately hitting several roadblocks along the way, as well as having increased overhead on the host system with every track change a new image needs to be created.

**Additional context**

Start by locating the online_image implementation in the ESPHome codebase and inspect how its current PNG handling works. Determine the project’s supported image-decoding path and tests before implementing JPG input; done means online_image can load the JPG entity_image described here without requiring host-side conversion.

Written by the indexing model from the issue text.