First-run setup: upload Bills_Tracker.xlsx and loader_rules.json from the web page when the data folder is empty

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app_dashboard.html

@@ -155,6 +155,7 @@ function renderTx(all){
 }
 async function init(){
   const j=await (await fetch("/api/data")).json();if(j.error){document.body.innerHTML="<main>"+esc(j.error)+"</main>";return}
+  if(j.setup){document.body.innerHTML=`<main><h1>Bills Dashboard</h1><p>Bills_Tracker.xlsx isn’t in the data folder (<code>${esc(j.data_dir)}</code>) yet. <a href="/">Upload it on the Statement Loader page.</a></p></main>`;return}
   D=j;$("#updated").textContent="Workbook saved "+j.updated;
   const yrs=[...new Set(j.tx.map(t=>+t[0].slice(0,4)))].sort().reverse();
   $("#year").innerHTML=yrs.map(y=>`<option>${y}</option>`).join("");