Add blank workbook template, example rules file, and Create blank workbook button

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

app_page.html

@@ -68,7 +68,8 @@ async function refresh(msg){
   const r=await fetch("/api/state");const s=await r.json();
   if(s.error){alertBox("bad",esc(s.error));return}
   if(s.setup){$("#coverage").innerHTML="";$("#preview").innerHTML="";$("#import").disabled=true;
-    $("#summary").innerHTML="";alertBox("warn",`<b>First-time setup:</b> <code>Bills_Tracker.xlsx</code> isn’t in the data folder (<code>${esc(s.data_dir)}</code>). Drop it into the box above (or copy it into that folder), then reload.`+(s.rules?"":" Also add <code>loader_rules.json</code> if you have one (your name, so transfers between your accounts are recognized)."));return}
+    $("#summary").innerHTML="";alertBox("warn",`<b>First-time setup:</b> <code>Bills_Tracker.xlsx</code> isn’t in the data folder (<code>${esc(s.data_dir)}</code>). Drop your existing one into the box above, or <button id="blank" style="margin-left:6px">Create a blank workbook</button>`+(s.rules?"":" Also add <code>loader_rules.json</code> (see loader_rules.example.json: your name, so transfers between your own accounts aren’t counted as spending)."));
+    const b=$("#blank");if(b)b.onclick=async()=>{try{const j=await post("/api/create_blank","");await refresh(esc(j.message))}catch(e){alertBox("bad",esc(e.message))}};return}
   s.bad.forEach(b=>alertBox("bad",`<b>${esc(b.file)}</b>: the transactions I read add up to ${fmt(b.parsed)} but the statement says ${fmt(b.stated)}. It will <b>not</b> be imported until that matches.`));
   s.skipped.forEach(b=>alertBox("warn",`<b>${esc(b.file)}</b>: ${esc(b.why)}`));
   s.duplicates.forEach(b=>alertBox("warn",`<b>${esc(b.file)}</b> is a duplicate of ${esc(b.same_as)}; counted once.`));