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_6_05-pasngr.js

@@ -5,6 +5,7 @@ import { absoluteRangeKeys, canTargetEnemy } from '../../../targeting.js';
 import { CHAIN_RADIUS } from '../../../constants.js';
 import { bodyDist, bodyInKeys } from '../../../body.js';
 import { num, bv, tbb, live, ANY, enemiesIn, batOf, N4, aura } from '../shared/tier6.js';
+import { powi } from '../../../detmath.js';
 
 // ------------------------------------------------------------------------------------------------------------------
 // 异客 chess_char_6_05 (链术师) — S3 辉煌裂片; 机理分析; 孤卒
@@ -25,7 +26,7 @@ function pasngr(bb, chess, def) {
     for (let i = 0; i < count && prev; i++) {
       hit.add(prev.id);
       battle.fx('lightning', { x: prev.x, y: prev.y, id: prev.id, src: unit.id });
-      battle.dealDamage(unit, prev, { amount: unit.s.atk * scale * Math.pow(1 - num(ch.falloff, 0.15), i), type: 'arts', isSkill: true, isAttack: true, tags: ['skill', 'storm'] });
+      battle.dealDamage(unit, prev, { amount: unit.s.atk * scale * powi(1 - num(ch.falloff, 0.15), i), type: 'arts', isSkill: true, isAttack: true, tags: ['skill', 'storm'] });
       if (slug > 0 && prev.alive) battle.applyStatus(prev, 'sluggish', { duration: slug, source: unit });
       let best = null, bd = Infinity;
       for (const x of battle.foesInRadius(prev.x, prev.y, ch.radius || CHAIN_RADIUS)) {