Use single quotes in Sass fallback error message

Switch error string from template literal to single quotes for
consistency with repo style (Prettier singleQuote). No behavioral
change; build and lint remain green.

Author: PeterDaveHello

build.mjs

@@ -96,7 +96,7 @@ async function runWebpack(isWithoutKatex, isWithoutTiktoken, minimal, sourceBuil
       const mod = await import('sass')
       sassImpl = mod.default || mod
     } catch (e2) {
-      throw new Error(`No Sass implementation available. Install 'sass-embedded' or 'sass'.`)
+      throw new Error("No Sass implementation available. Install 'sass-embedded' or 'sass'.")
     }
   }