Shape the cone by hand, and give the playground its knobs back

Oliver's tuned numbers become the defaults: beamY 0.95, beamLen 23, beamW0 0.08,
beamW1 3.1, beamOriginLift 0.44, beamBorder 0.18.

Three knobs earned their keep on the way there.

beamLen is the DRAWN length now, not only the kill range. The drawn length was
solved every frame so the far end landed on the middle of the ad strip, which
made this a control that visibly did nothing. One meaning beats one clever
behaviour -- and it pairs with beamY, since a lower plane meets the ads sooner.

beamOriginLift replaces beamOriginY: the apex is a lift ABOVE the plane rather
than an absolute height, so lowering beamY brings the near end down with it
instead of leaving it hanging at chest height with the beam sloping away.

beamBorder exposes the edge width, which was hardcoded.

And the playground is back, deliberately NOT paused. The first version froze the
world so the picture would hold still, and then nothing redrew, so every value
changed did nothing -- a still frame you cannot change is worth nothing. The
bodies are held still individually and spawning is off instead.

Also: a boolean living in TUNE has to be tested with >= 0.5. The panel steps
every key by 0.02, so one nudge set beamBand to 0.02 -- still truthy -- and the
renderer switched variants under him mid-tune.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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