feat(ludic.lab): the visual lab as a package - a scene on a plate, never a world

A scene is an entry in the open registry LabScenes, shown on a plate: a
flat lit disc, the package's own small sky with the sun at one hour, and
a frame clock. Headless each camera (lab_shot, lab_shot_at) settles and
is written as build/lab/<scene>/<shot>.png (a stored PNG, written here);
in a window N and P step through them. tools/lab/run.sh and sheet.py
make the contact sheet; tools/lab/plate_build.py makes plate/.
ludic.render3d gains r3d_plate_mode (no terrain, grass or water is made)
and r3d_sky_path. quit() in a program with no frame loop links. The
example takes ~120 MB resident, 417 MiB peak footprint. Reseed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/lab/sheet.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+"""sheet.py DIR [DIR ...] - a contact sheet of a lab scene's shots: DIR/sheet.png, the PNGs in DIR
+(sheet.png itself excepted) in name order, two to a row at 640 wide, each captioned with its name."""
+import glob, os, sys
+from PIL import Image, ImageDraw
+
+def sheet(out):
+    paths = [p for p in sorted(glob.glob(os.path.join(out, '*.png'))) if os.path.basename(p) != 'sheet.png']
+    if not paths:
+        print(f'lab: {out}: no shots')
+        return 1
+    ims = [Image.open(p).convert('RGB') for p in paths]
+    w = 640
+    h = w * ims[0].height // ims[0].width
+    cols = 2 if len(ims) > 1 else 1
+    rows = (len(ims) + cols - 1) // cols
+    s = Image.new('RGB', (w * cols, h * rows), (0, 0, 0))
+    d = ImageDraw.Draw(s)
+    for i, (p, im) in enumerate(zip(paths, ims)):
+        x, y = (i % cols) * w, (i // cols) * h
+        s.paste(im.resize((w, h)), (x, y))
+        d.rectangle((x, y, x + w, y + 18), fill=(0, 0, 0))
+        d.text((x + 6, y + 3), os.path.splitext(os.path.basename(p))[0], fill=(255, 255, 255))
+    s.save(os.path.join(out, 'sheet.png'))
+    print(f'lab: {out}: {len(ims)} shots, sheet.png')
+    return 0
+
+if __name__ == '__main__':
+    sys.exit(max([sheet(d) for d in sys.argv[1:]] or [2]))