Clearer content warning button in the composer

[mary-ext]

Is your feature request related to a problem? Please describe.

It's not immediately clear that you can manually add content warning to images and videos, lots of NSFW content gets posted to Bluesky without the appropriate content warning attached.

While Bluesky's auto-moderation can usually get to them, we shouldn't teach users to heavily rely on this behavior. Automod does not happen immediately, and it's also not perfect.

Describe the solution you'd like

Move the content warning button to be below the image/video, and make it really apparent. Below is an example.

Describe alternatives you've considered

NUX might teach users but I don't think it's something that should only be shown once kind of thing.

Additional context

N/A