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/body.js

@@ -24,6 +24,7 @@
 // `hitRect`).
 
 import { ROWS, COLS } from './constants.js';
+import { hypot } from './detmath.js';
 
 /**
  * Validated hit area of a data record (`{ w, h, dx, dy }`, tiles) or null for a regular (point) unit.
@@ -83,10 +84,10 @@ export function bodyInKeys(u, keys) {
 /** Distance (tiles) from point (x, y) to the unit's body: its position, or its rectangle (0 inside). */
 export function bodyDist(u, x, y) {
   const R = hitRect(u);
-  if (!R) return Math.hypot(u.x - x, u.y - y);
+  if (!R) return hypot(u.x - x, u.y - y);
   const dx = x < R.x0 ? R.x0 - x : x > R.x1 ? x - R.x1 : 0;
   const dy = y < R.y0 ? R.y0 - y : y > R.y1 ? y - R.y1 : 0;
-  return Math.hypot(dx, dy);
+  return hypot(dx, dy);
 }
 
 /** Is the unit's body within `r` tiles of point (x, y)? (the same ≤ r + 1e-9 test as Battle.enemiesInRadius) */