Add auto-captions to videos

Give users the ability to toggle on/off adding "baked-in" captions their generations, using multiple places to control these settings:

• Initial Setup: set account-wide default for captions (update in account settings)

• Collection Link: override default settings for all videos using that link

• Individual Video: override caption settings for that specific video & regenerate

Give users a default choice of popular caption styles, or customize their own.

Also possibly explore using basic closed caption toggle on video player using transcript, for videos that don't have captions included.