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-mcnist.js

@@ -58,6 +58,7 @@
 import { num, skillRec, batMod, up } from '../shared/tier1.js';
 import { COLS } from '../../../constants.js';
 import { dirVec } from '../../../dir.js';
+import { hypot } from '../../../detmath.js';
 
 const S1 = 'skchr_mcnist_1';
 const S2 = 'skchr_mcnist_2';
@@ -197,7 +198,7 @@ function grafKit(owner, { life, t2, b2, b3, aura }) {
 function chargeGraf(battle, mcn, t, b3) {
   if (!up(t)) return;
   const { stop, land } = chargeEnd(battle, t);
-  const dist = Math.hypot(stop[0] - t.tileR, stop[1] - t.tileC);
+  const dist = hypot(stop[0] - t.tileR, stop[1] - t.tileC);
   t.mem.charging = true;
   battle.fx('charge', { x: t.x, y: t.y, id: t.id, tx: stop[1], ty: stop[0] });
   battle.retreat(t, { reason: 'expired', permanent: true });