Add image_analysis/beam_stop/ShadowFinder.{h,cpp} and SHADOW_FINDER.md: a
self-contained beam-stop shadow detector that accumulates images via AddImage()
and returns a mask from GetMask(), mirroring the shape of DarkMaskAnalysis.
It detects the beam-stop shadow (central disk + holder arm) as an azimuthal
anomaly: an iterated radial-median background baseline, a ratio threshold, a
connectivity-to-beam-centre anchor with module-gap bridging, a central low-res
disk guard capped just inside the innermost reflection, and a reflection guard
that never masks a pixel that recorded real signal.
Not yet wired: not added to image_analysis/CMakeLists.txt and no PixelMask /
Rugnux / viewer changes. SHADOW_FINDER.md documents the algorithm and the
deferred offline (Rugnux bit 9 + viewer user-mask) integration plan.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 4.8
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