fix: getPipCount used non-existent VARIANTS.standard key

The VARIANTS object has keys 'sheshbesh', 'mahbousa', 'thirtyone' but
getPipCount referenced 'standard' which is undefined, causing
'Cannot read properties of undefined (reading normPos)' and preventing
the entire board from rendering.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/js/modules/backgammon/logic/rules.js

@@ -264,7 +264,7 @@ export function getGameScore(state, winner, rule) {
 }
 
 export function getPipCount(state, type) {
-  const rule = VARIANTS.standard;
+  const rule = VARIANTS.sheshbesh;
   let pips = 0;
   for (let i = 0; i < 24; i++) {
     const count = countAtPos(state, i, type);