gallery upload: add FileReader + img error handlers

- reader.onerror: shows error message on file read failure
- img.onerror: detects unsupported image formats (HEIC, RAW)
- Shows clear feedback: 'unsupported format' or 'format not supported'
- Helps diagnose gallery upload issues

static/index.html

@@ -2615,9 +2615,20 @@
 
       // Show thumbnail in scan photo preview
       const reader = new FileReader();
+      reader.onerror = function() {
+        const ocrEl = document.getElementById('scanOcrResult');
+        if (ocrEl) ocrEl.textContent = '❌ Could not read file — unsupported format or corrupted. Try a JPEG screenshot instead.';
+        const preview = document.getElementById('scanPhotoPreview');
+        if (preview) preview.style.display = 'block';
+      };
       reader.onload = async function(e) {
         const thumb = document.getElementById('scanPhotoThumb');
         if (thumb) thumb.src = e.target.result;
+        thumb.onerror = function() {
+          const ocrEl = document.getElementById('scanOcrResult');
+          if (ocrEl) ocrEl.textContent = '❌ Image format not supported in browser. Try a JPEG screenshot.';
+          thumb.style.display = 'none';
+        };
 
         const preview = document.getElementById('scanPhotoPreview');
         if (preview) preview.style.display = 'block';