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_3_04-swire2.js

@@ -7,6 +7,7 @@ import {
   num, defOf, talentBb, moduleTalentBb, selectedId, altSkills, alive, gridKeys, fx, copyGrid, textNum, freeTile,
   groundTile, enemiesOn,
 } from '../shared/tier3.js';
+import { powi } from '../../../detmath.js';
 
 /** 琳琅诗怀雅 S3's coin range (PRTS 备注 "前方范围2-4"; range_table "2-4", facing right). */
 const SWIRE2_COIN_GRID = Object.freeze([[1, 1], [0, 0], [0, 1], [0, 2], [-1, 1]]);
@@ -267,7 +268,7 @@ export default {
           battle.on('fatal', (ctx) => {
             if (ctx.unit !== unit || ctx.prevented) return;
             const n = unit.mem.saveCount ?? 0;
-            const cost = Math.abs(num(t1.cost, -5)) * Math.pow(num(t1.cost_multi, 2), n);
+            const cost = Math.abs(num(t1.cost, -5)) * powi(num(t1.cost_multi, 2), n);
             const pl = battle.getPlayer(unit.ownerId);
             if (!pl || pl.dp + 1e-9 < cost) return;
             battle.addDp(unit.ownerId, -cost);