Fix slug lookup and add regression test

hdyc-svelte/src/lib/data/calculators.ts

@@ -3167,6 +3167,11 @@ export const calculators: CalculatorDef[] = [
 
 ];
 
+const slugIndex: Map<string, CalculatorDef> = new Map(
+    calculators.map(calc => [calc.slug, calc])
+);
+
+
 export function getCalculatorBySlug(slug: string): CalculatorDef | undefined {
   return slugIndex.get(slug);
 }