Feat/grayscale photo endpoint

[gsrunion]

No description provided.

[esto-openscan]

Thanks for the detailed work. Capturing and exposing grayscale jpegs is a good direction to extend the API! Before merging I spotted two blockers and one design concern:

1. capture_grayscale_jpeg() bypasses the EXIF flow from capture_jpeg(), so the grayscale files miss orientation/metadata. Photogrammetry pipelines usually rely on that, so we should inject at least the existing Orientation/Model fields (or document why not).
2. Cropping settings aren’t applied for grayscale captures. _configure_cropping_for_scalercrop() is only used by capture_jpeg(). That makes grayscale outputs ignore the user’s crop configuration.
3. Design-wise, a boolean grayscale query param will not scale once we add more formats. Passing the format directly (e.g., image_format=jpeg|grayscale_jpeg|…) would align with Controller.photo_async(image_format=…) and avoids future parameter creep.

Let me know if I can help with the follow-ups!