Explorer: six UI items + genre-tool learns the star chart

Paul's batch, all headless-verified with 0 console errors:

• 1. Zoomed edge-reach FIXED: PAN_PAD was screen-space but far too small (0.18 let an edge star reach only 18% in from the rim). 0.55 lets every corner star reach dead center

• genre-tool.js: create now REQUIRES spec.pos [x,y] and splices it into explorer.html's new /* genre-tool:positions */ block

Verified: live smoke PASS (load 0.987, balance 0.936, 0 errors); verify.sh PASS; genre-tool check hogcore self 100 unchanged.

▶ Play it: Perihelion Squeal → Barometric Stampede → Inclement Surveillance — the three genres this change names, as one path https://stellate.app/?genre=hogcore&seed=8848&path=1670.17099,1718.20526,388.8037&xdur=0.06

decc543 https://github.com/aboard-io/stellate/commit/decc5430e5de71203263ed77bda3555875c0df0c