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>

packages/ludic.lab/state.ludic

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+# state.ludic - which scene, its shots, and where the loop is in them
+var lb_scene: string = ""
+var lb_frame: int = 0
+var lb_shot_names: []string = null
+var lb_shot_pose: []float = null    # 5 per shot: x, y, z, yaw and pitch in degrees
+var lb_shot: int = 0                # the shot being taken or looked at
+var lb_wait: int = 0                # frames held on it so far
+var lb_settle: int = 45             # frames a shot is held before it is taken
+var lb_out: string = ""             # build/lab/<scene>
+var lb_windowed: bool = false
+var lb_note: string = ""            # one line a scene may show under its title
+var lb_font: string = ""            # an overlay font atlas directory; "" draws no captions
+var lb_title: string = "Ludic Lab"
+var lb_draw: fn() = null            # the scene's own drawing, beside the actors
+var lb_shots_taken: int = 0
+
+# frames a shot settles before it is taken (streaming, auto-exposure); 45 by default
+export function lab_settle(frames: int) -> void { lb_settle = Math.max(1, frames) }
+# the overlay's font atlas (a directory with font.json and font.png) for the captions
+export function lab_font(dir: string) -> void { lb_font = dir }
+export function lab_title(title: string) -> void { lb_title = title }
+# one line under the scene's title in a window
+export function lab_note(s: string) -> void { lb_note = s }
+# the scene being shown, and the frame the clock is on (60 a second, whatever the machine)
+export function lab_scene() -> string { return lb_scene }
+export function lab_frame() -> int { return lb_frame }
+export function lab_time() -> float { return float(lb_frame) / 60.0 }