Files in one DCF directory that share a file number are one file group,
as section 4.3.2.2 of the specification says. `Directory.FileGroups`
lists them, each with its numbers, its members and its primary member. A
lone file is a group of one. A group reports its member count and total
size.
Section 6.2.1.3 gives a DCF basic file priority over a DCF extended image
file. It says nothing about a DCF optional file, so ranking every `JPG`
first is a choice. A `THM` comes last.
`isImageFile` now accepts `.tif`, so a `TIF` counts as an image.
`Store.Images`, `Store.Videos` and the totals still count each file on
its own.
Model: opus-5-5
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>
clawbot
cf7611ea1b