The label-visibility zoom threshold (was the LABELS_CAMERA_RATIO=1
constant) becomes the fourth persisted setting: labels appear when the
camera ratio is at/below it (1x = fit zoom; slider 0.5x-4x, shown with
an x suffix). Deliberately THE single zoom knob per the cluster design
(vision section 1): cluster labels will fade in over the same span as
node labels fade out, gated inversely on this same setting.
Live-verified: at a zoomed-out camera (labels previously hidden),
raising the threshold to 4x rebuilds and re-shows labels without any
camera movement; resetting restores the fade. 355/355 tests,
typecheck, lint clean.
amosblomqvist
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