Merge the drill lane fix and the rate-gate sample size into staging

index.html conflicted only on the cache-buster: staging was at 276 and the
branch at 275, so the merge takes 277 — a merge that reuses either number
leaves phones on the old build.

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

src/config.js

@@ -461,7 +461,6 @@ export const TUNE = {
   drillSeed: 4,     // bodies placed at the start so there is a queue to read from the first second
   drillSeedGap: 2.6,// m of depth between those seeded bodies
   drillSpawnZ: 0.6, // z they enter at (the far baseline is 0)
-  drillNearZ: 9.0,  // spawn spacing is measured against bodies nearer than this
   drillSpread: 3.4, // m either side of the centre line the lanes fan across
   drillSpeed: 0.85, // m/s at the bottom of the ramp (x the type's vMul)...
   drillSpeedMax: 2.0,// ...and at the top. Stamped per body AT SPAWN — constant v is also what lets