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/enemies/helpers.js

@@ -6,6 +6,7 @@
 import { ELEMENT } from '../../constants.js';
 import { canTargetAlly, sortAllyTargets, areaSelectable, auraSelectable } from '../../targeting.js';
 import { mitigate } from '../../damage.js';
+import { hypot } from '../../detmath.js';
 
 // ---------------------------------------------------------------------------------------------------------------
 // constants (numbers that exist nowhere in the data)
@@ -295,7 +296,7 @@ export function spawnChildren(b, parent, key, n, opts = {}) {
 /** Move a unit straight toward (tx, ty) by `dist` tiles. Returns true on arrival. */
 export function stepToward(u, tx, ty, dist) {
   const dx = tx - u.x, dy = ty - u.y;
-  const d = Math.hypot(dx, dy);
+  const d = hypot(dx, dy);
   if (d <= dist + 1e-9) { u.x = tx; u.y = ty; return true; }
   u.x += (dx / d) * dist;
   u.y += (dy / d) * dist;