Accept images and image folders in the CLI

[FreeApophis]

vcs only spoke video while the library had grown an image pipeline. It now takes folders and
image files too, detected from the input itself rather than through a new verb or a mode flag.

vcs holiday/                          # one sheet from the folder -> holiday.png
vcs holiday/ --recursive --all        # every image, subfolders included
vcs holiday/ --fit cover -c 5 -r 4    # crop to fill the cells instead of letterboxing
vcs holiday/*.jpg -o summer.jpg -f jpg
vcs clip.mp4 holiday/                 # two sheets, one per input

Detection order is Directory.Exists, then a known image extension, then video — so anything
that resolved to video before still does, unusual containers included.

The awkward part

The positional argument means "one input → one sheet" for video, but N images make one sheet.
InputResolver owns that asymmetry: a video and a directory each get their own sheet, while loose
image files coalesce into a single group that takes the position of the first one.

vcs a.mkv one.jpg b.mkv two.jpg
  → [ a.mkv ] [ one.jpg + two.jpg ] [ b.mkv ]      3 sheets

It also expands wildcards itself, since cmd and PowerShell hand them through verbatim unlike a
POSIX shell — so vcs holiday/*.jpg behaves identically on every platform.

New options

--recursive, --fit <contain|cover|stretch> and --all, mirroring the library knobs, plus a
matching [image] section in the TOML config. Everything else already applied to both media.
--timestamp is now described as the caption overlay, since for images it carries the file name.

No short alias for --recursive: -r is already --rows, and -r/-R differing only in case
is a footgun on a tool where both are plausible.

Misapplied options are errors

$ vcs holiday/ --interval 3m30
--interval applies to video inputs only.          # exit 1

$ vcs clip.mp4 holiday/ --interval 3m30           # fine — applies to the video

The difference between a typo and a sheet that quietly ignored what you asked for. Mixed runs are
exempt, since there each option legitimately applies to part of the input.

Structure

InputResolver (detection + grouping + globbing), OptionScopeValidator (scope rules),
ImageOptionsFactory (config→CLI layering + collection construction), and SheetRunner switching
on the kind. Video and ImageCollection already expose the same SaveContactSheetAsync shape,
so the runner needed a switch rather than an abstraction over two cases.

Verification

36 new tests (112 total, all passing), clean under -warnaserror. Beyond the unit tests, run
against the real binary with a 16-photo folder:

Case	Result
vcs <folder>	16-image sheet
vcs '03*.jpg' from cmd-style invocation	glob expanded by the CLI, 9 images
vcs sample.mp4 photos -i 5	two sheets, sample.png + photos.png, interval applied to the video only
vcs <folder> --interval 3m30	error, exit 1
vcs sample.mp4 --fit cover	error, exit 1
vcs sample.mp4	unchanged, exit 0
--all vs sampling at -c 4 -r 2	4 rows (483px) vs 2 rows (305px)
--fit cover	portraits cropped to fill, no letterbox bars
[image] config via --config	round-trips through Tomlyn; invalid value names the config as the source

Supersedes the "CLI covers video only for now" line from #25.

🤖 Generated with Claude Code