Duration-as-time slider, void-blend evolution, and add/remove-nodes fix

DURATION SLIDER — the loop's travel is now dialed directly as a TIME — 8 min to 24 h on a log slider, default 30 min — replacing the abstract bars-per-leg "pace".

VOID-BLEND — the genre mix used to pin ONE genre at 100% across any sparse region — a path drawn through empty space then played the same genre for hours (Paul's ?path sat on canawave ~20 min).

ADD/REMOVE NODES — double-tap-to-add/remove had stopped working — the two-tap proximity was measured in LOGICAL world units (<16), but the map spans ~25000 units tall, so at default zoom that window was ~0.4 SCREEN px: no finger…

• simulate-path.js: the auto walk length is now loopBars() (one full loop at the current speed) instead of pace×legs, which under the duration model no longer completes a loop.

Verified: simulate-path 4/4 (all 3 default genres crossed), share-url 13/13 (legacy pace URL maps identically), explorer-ui constant-pace seamless, full-boot healthy.

▶ Play it: Loon Referendum — parked on the genre this change names https://stellate.app/?genre=canawave&seed=6696&path=1505.3698,1524.3731,1486.3731&xdur=13.122

39c0a9d https://github.com/aboard-io/stellate/commit/39c0a9d0b9680d70ea2d22698fe1c786381db36b