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-poca.js

@@ -36,6 +36,7 @@
 
 import { num, talentBb, moduleBb, moduleOn, traitBb, skillRec, statBuff, onHitBy, enemiesInGrid, up } from '../shared/tier1.js';
 import { hasHp } from '../../../damage.js';
+import { hypot } from '../../../detmath.js';
 
 const S1 = 'skcom_atk_up[3]';
 const S2 = 'skchr_poca_2';
@@ -161,7 +162,7 @@ export default {
         if (ds > 0) {
           onHitBy(battle, unit, ({ target, dmg }) => {
             if (!dmg.isAttack) return;
-            const d = Math.hypot(target.x - unit.x, target.y - unit.y);
+            const d = hypot(target.x - unit.x, target.y - unit.y);
             dmg.mul *= 1 + ds * Math.max(0, Math.min(1, (d - lo) / Math.max(1e-6, hi - lo)));
           });
         }