2725a9b3

By: Michael Lynch <git@mtlynch.io>

Make MediaConverter a func-backed struct in uploads

Replace the MediaConverter interface and main's local adapter with a struct of
two conversion funcs defined in the uploads package, so main constructs it
directly:

  uploads.MediaConverter{
      ConvertPhoto:         images.StripMetadata,
      ConvertAnimatedPhoto: convert.WriteGIFToAnimatedAVIF,
  }

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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