feat: improve zoom montage QC PNGs — better mask color, no-mask output, n4 bg option

[Copilot]

The ROI zoom montage QC figures had a yellow mask overlay (hard to see on grayscale), produced only one output per run, and always used the raw SPIM as background.

Changes

Mask overlay color

• Changed colormap from "spring" (yellow) → "Reds" (red), which is visually distinct on grayscale SPIM data

No-mask output

• Each qc_segmentation_roi_zoom / qc_vessels_roi_zoom rule now produces two PNGs:
  • ..._desc-{desc}_roimontage.png — with red mask overlay (unchanged filename)
  • ..._desc-{desc}nomask_roimontage.png — raw SPIM, no overlay
• nomask suffix on the desc entity ensures the two files are adjacent in alphanum sort
• Crops are cached so the second figure is generated with no additional I/O

N4-corrected background (--qc_roi_zoom_bg_n4)

• New CLI flag; when set together with --correction_method n4, uses the N4 bias-field corrected OME-Zarr as the background image instead of raw SPIM
• The corrected zarr is added as an explicit Snakemake input only when the flag is active, preserving normal dependency tracking

spimquant bids/ out/ participant \
  --correction_method n4 \
  --qc_roi_zoom_bg_n4

Files changed

File	Change
workflow/scripts/qc_segmentation_roi_zoom.py	Color, dual outputs, n4 bg path, DPI standardized to 150
workflow/rules/qc.smk	png_nomask output, conditional spim_n4 input, use_n4_bg param
workflow/Snakefile	No-mask targets added to all_participant for seg and vessel
config/snakebids.yml	--qc_roi_zoom_bg_n4 CLI option