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/chess_char_4_01-rmixer.js

@@ -7,6 +7,7 @@ import {
   AURA, num, tbb, grid, nationOf, enemiesOnRange, targetsInRange, whileDeployed, reveal, skillActive, isSel, alt,
   instantKind, withDefaults,
 } from '../shared/tier4.js';
+import { hypot } from '../../../detmath.js';
 
 /** Is module `id` the active one? (elites; `'none'` / normal chess ⇒ false) */
 const moduleIs = (def, id) => !!(def?.raw?.module?.active && def.raw.module.id === id);
@@ -39,7 +40,7 @@ export default withDefaults({
               const n = num(bb.charge, 1);
               const cand = battle.alliesInRadius(unit.x, unit.y, 1.5, unit.ownerId)
                 .filter((a) => a !== unit && a.kind === 'op' && nationOf(a) === 'laterano' && a.skill && a.skill.active && a.skill.kind === 'ammo')
-                .sort((a, b) => Math.hypot(a.x - unit.x, a.y - unit.y) - Math.hypot(b.x - unit.x, b.y - unit.y) || a.id - b.id);
+                .sort((a, b) => hypot(a.x - unit.x, a.y - unit.y) - hypot(b.x - unit.x, b.y - unit.y) || a.id - b.id);
               if (!cand[0] || !(n > 0)) return;
               cand[0].skill.addAmmo(n);
               battle.fx('reload', { x: cand[0].x, y: cand[0].y, id: cand[0].id, n });