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_02-sbell2.js

@@ -4,6 +4,7 @@
 import { COLS } from '../../../constants.js';
 import { bodyInKeys } from '../../../body.js';
 import { num, tbb, moduleBb, live, keyOf, enemiesIn, isTok, instantKind, AROUND8, aura } from '../shared/tier6.js';
+import { hypot } from '../../../detmath.js';
 
 // ------------------------------------------------------------------------------------------------------------------
 // 圣聆初雪 chess_char_6_02 (阵法术师) — S3 群山俯首; 无垠的雪景; 圣山的祝福; module 千分之一的心
@@ -217,7 +218,7 @@ function lureGoal(battle, unit, e) {
   for (const [dr, dc] of AROUND8) {
     const r = unit.tileR + dr, c = unit.tileC + dc;
     if (!battle.grid.groundPassable(r, c)) continue;
-    const d = Math.hypot(e.x - c, e.y - r);
+    const d = hypot(e.x - c, e.y - r);
     if (d < bd - 1e-9) { bd = d; goal = [r, c]; }
   }
   return goal;