Canvas shadow-blur was ~100x more expensive per draw than a plain stroke.
With globalOverrideEnabled=true, every visible node drew a shadow-blurred
rect every frame, tanking framerate. Replaced with a two-pass strokeRect
(wide low-alpha + thin core) for the same visual but 100x cheaper.
Also lowered heavyThemeNodeBudget default 60 -> 25 so motion is gated
sooner on heavier graphs.
IxMxAMAR
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