Compress photos on upload to fit Excel 32,767-char cell limit

- Add compressImage(): resize to max 400px width, JPEG quality 0.5
- Replace FileReader with canvas-based compression in handlePhotoUpload
- Add try-catch in export with alert on overflow

index.html

@@ -458,12 +458,29 @@ function esc(s) {
 // ═══════════════════════════════════════════════════════════
 // ─── Photo ─────────────────────────────────────────────
 // ═══════════════════════════════════════════════════════════
-function handlePhotoUpload(flagId, file) {
+function compressImage(file, maxW = 400, quality = 0.5) {
+  return new Promise((resolve) => {
+    const img = new Image();
+    const url = URL.createObjectURL(file);
+    img.onload = () => {
+      URL.revokeObjectURL(url);
+      let w = img.width, h = img.height;
+      if (w > maxW) { h = h * maxW / w; w = maxW; }
+      const c = document.createElement('canvas');
+      c.width = w; c.height = h;
+      const ctx = c.getContext('2d');
+      ctx.drawImage(img, 0, 0, w, h);
+      resolve(c.toDataURL('image/jpeg', quality));
+    };
+    img.src = url;
+  });
+}
+
+async function handlePhotoUpload(flagId, file) {
   const flag = flags.find(f => f.id === flagId);
   if (!flag || !file) return;
-  const reader = new FileReader();
+  flag.photoData = await compressImage(file);
-  reader.onload = (e) => { flag.photoData = e.target.result; renderList(); };
+  renderList();
-  reader.readAsDataURL(file);
 }
 
 function removePhoto(flagId) {
@@ -692,10 +709,16 @@ document.getElementById('export-btn').addEventListener('click', () => {
     Photo: f.photoData ?? '',
   }));
   const wb = XLSX.utils.book_new();
-  const ws = XLSX.utils.json_to_sheet(rows);
+  const ws = XLSX.utils.json_to_sheet(rows, { cellDates: true });
   ws['!cols'] = [{ wch: 12 }, { wch: 20 }, { wch: 10 }, { wch: 12 }, { wch: 12 }, { wch: 60 }, { wch: 30 }];
   XLSX.utils.book_append_sheet(wb, ws, 'Flags');
+  try {
     XLSX.writeFile(wb, 'flag_export.xlsx');
+  } catch (e) {
+    if (e.message?.includes('32767')) {
+      alert('Photo data is too large. Try uploading smaller photos.');
+    } else { throw e; }
+  }
 });
 
 // ═══════════════════════════════════════════════════════════