screenshots: frame 10 dmabuf-wayland green capture (reference for #1)

Reference image of the bug as visible on ohm. Captured 2026-05-08 via
mpv --hwdec=v4l2request --vo=dmabuf-wayland --pause --start=00:00:00.42
--fullscreen fourier-test/bbb_1080p30_h264.mp4 then spectacle -b -f -n.

Uniform dark green at approx RGB(0, 75, 0) — exactly what the all-zero
NV12 hypothesis (Y=U=V=0 through BT.601/709 conversion) predicts and
what marfrit/dmabuf-modifier-triage#1 diagnoses (KWin reads past-EOF
on the UV plane fd, returns zeros for chroma).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

screenshots/README.md

@@ -0,0 +1,11 @@
+# Screenshots
+
+Reference captures of the user-visible bug. Filed alongside `phase0_findings.md` so future readers see the symptom directly without reproducing it.
+
+## frame10_dmabuf_green.png
+
+`mpv --hwdec=v4l2request --vo=dmabuf-wayland --pause --start=00:00:00.42 --fullscreen fourier-test/bbb_1080p30_h264.mp4` on ohm, frame ~10 of `bbb_1080p30_h264.mp4` (24 fps), captured via `spectacle -b -f -n` 2026-05-08.
+
+Shows uniform dark green fill where the bbb test pattern should be. Black bars top/bottom are letterboxing from fullscreen presentation on PineTab2's 1280×800 display vs the 1920×1080 / 16:9 source — they're not part of the bug.
+
+The dark green color is approximately RGB(0, 75, 0), which matches the predicted output of an all-zero NV12 buffer (Y=0, U=0, V=0) through BT.601/709 → RGB conversion. Confirms the [marfrit/dmabuf-modifier-triage#1](https://git.reauktion.de/marfrit/dmabuf-modifier-triage/issues/1) diagnosis: KWin reads UV plane past-EOF on its `fd 42`, gets zeros, renders dark green.