Use variable name & period in name of XLSX file

src/routes/variables/[variable]/xlsx/+page.svelte

@@ -15,6 +15,7 @@
   import XLSX from "xlsx-js-style"
 
   import { browser } from "$app/environment"
+  import { page } from "$app/stores"
   import { calculationNames, type CalculationByName } from "$lib/calculations"
   import { entityByKey } from "$lib/entities"
   import {
@@ -56,6 +57,8 @@
   const webSocketOpenByName: WebSocketOpenByName = {}
   const year = getContext("year") as Writable<number>
 
+  $: ({ variable: requestedVariableName } = $page.params)
+
   $: ({ variables } = data)
 
   $: if (browser) {
@@ -66,7 +69,11 @@
     calculationByName !== undefined &&
     !Object.values(calculationByName).some(({ running }) => running)
   ) {
-    generateWorkbook(variables, valuesByCalculationNameByPeriodByVariableName)
+    generateWorkbook(
+      requestedVariableName,
+      variables,
+      valuesByCalculationNameByPeriodByVariableName,
+    )
   }
 
   function calculate(variables: Variable[]) {
@@ -212,6 +219,7 @@
   }
 
   async function generateWorkbook(
+    requestedVariableName: string,
     variables: Variable[],
     valuesByCalculationNameByPeriodByVariableName: ValuesByCalculationNameByPeriodByVariableName,
   ) {
@@ -391,7 +399,11 @@
       }
     }
 
-    XLSX.writeFile(workbook, "leximpact.xlsx", { compression: true })
+    XLSX.writeFile(
+      workbook,
+      `leximpact_${requestedVariableName}_${$year}.xlsx`,
+      { compression: true },
+    )
   }
 
   function openWebSocket() {