Feat: proportional adjustment of brightness

[Julien-Decoen]

This PR updates async_turn_on to apply brightness changes proportionally across each bulb, based on the difference between current and target brightness, creating smoother transitions in multi-bulb setups. I’ve also modified the devcontainer to simplify it—let me know if it works well on your end, or I can revert if needed!

[jseidl]

I think the idea is really cool. People might want the current behavior as well (absolute setting) so might be good to have an option to configure the group adjustment mode (absolute/relative). I can merge this PR after the release and then work out the option into it.

If you can split up this PR, I'd like to try out your devcontainer changes and merge as should be a quick thing to do. I also liked the improvements for "unspaghettifying" the color temp/rgb logic. I can manually copy those over if it's too much of a hassle separating it and I want to merge those parts of it for the next release which I intend to do next weekend.

Thanks a lot for all the PRs you've been submitting, really appreciate it!

[Julien-Decoen]

I just created two separate PRs: one for the configuration changes and another for the async_turn_on improvements.

I’ve also got some other cool features on my fork, like a lights_out feature that dims the room's brightness (where possible) 20 seconds before turning off the lights to give a heads-up. I’m also working on an automated dashboard to easily visualize and manage all entities created and controlled by Magic Areas. The main challenge right now is loading the JS file automatically when the custom component is instantiated. I’d be happy to chat more about these features if you’re interested!

Your custom component is really inspiring for the future of smart homes and Home Assistant—it simplifies managing a large number of devices. Thanks for all your hard work!