[BUILD-600] Fix: Web media not available in new anki profile

This fixes two issues related to media files in the ankkihub/gui/web/media folder. These media files define icons used for the AI features.

Proposed changes

Move _copy_web_media_to_media_folder to _profile_setup We were previously only adding the files to the Anki's media folder of the profile that Anki had when it was started. When switching to a new profile the media was not available, which led to icons not being shown, e.g. the smart search button icon.
Add underscore to icon file nameto prevent cleanup by Anki Anki has a media cleanup tool under Tools -> Check Media, which removes unused media. (Our media files are not used on any notes, so Anki doesn't know they are used somewhere.) Anki excludes files which start with an underscore from removal.