feedback7: the battle sim uses engine-independent math — Chrome, Firefox, Safari and the server agree bit for bit (PR #373 by @Cloudnyco)

- server/sim/detmath.js: hypot (sqrt of the squares, rescaled outside 2^±500), powi (integer powers in double-double,
  one rounding), sin / cos (fdlibm 5.3) and atan2 (fdlibm / FreeBSD msun) built only from correctly rounded IEEE
  operations; the sim's Math.hypot / sin / cos / atan2 / pow calls go through it (65 files); eslint.config.js forbids
  the approximated Math functions under server/sim and test/sim/detmath.test.js scans for them.
- sin / cos / atan2 are the algorithms V8 runs in Node, so the server's results stay; only hypot differs from V8's.
  Golden: 2 moved — diy-027 (a hypot distance, damage +80) and coop3-ABYSS-5 (a later card pick from round 9, same end).
- Applied unchanged after review (Grok static review: MERGE; the diff read in full: no network, no new dependency).
- Tests: broad node --test 5155 / 5155 with the new file tracked (detmath 7 / 7, package 10 / 10); lint 0 errors,
  typecheck, check:imports.

server/sim/content/kits/ops/op-mantra.js

@@ -46,6 +46,7 @@ import { hasHp } from '../../../damage.js';
 import { canTargetEnemy, enemyStealthed } from '../../../targeting.js';
 import { bodyInKeys } from '../../../body.js';
 import { COLS, PALSY_MAX } from '../../../constants.js';
+import { hypot } from '../../../detmath.js';
 
 const S1 = 'skchr_mantra_1';
 const S2 = 'skchr_mantra_2';
@@ -91,7 +92,7 @@ function nearestFoe(battle, unit, x, y, r, skip) {
   let best = null, bd = Infinity;
   for (const e of battle.enemiesInRadius(x, y, r)) {
     if (skip.has(e) || !canTargetEnemy(unit, e, ANY)) continue;
-    const d = Math.hypot(e.x - x, e.y - y);
+    const d = hypot(e.x - x, e.y - y);
     if (d < bd - 1e-9 || (Math.abs(d - bd) <= 1e-9 && best && e.spawnSeq < best.spawnSeq)) { bd = d; best = e; }
   }
   return best;