Fix iOS hang when selecting many photos

Root cause: FileReader.readAsDataURL() loads the entire file into memory
as a base64 string. With 50+ iPhone photos (3-12 MB each), this exceeds
iOS Safari's per-tab memory limit and freezes the tab.

Changes:
- Replace readAsDataURL with URL.createObjectURL(file) — zero-copy file
  reference, no memory bloat (static/index.html)
- Reduce batch size from 4 to 2 — gentler on memory-constrained devices
- Add URL.revokeObjectURL() on reset — prevent blob URL leaks
- Add HEIC/HEIF support to server.py — iPhone format compatibility

Closes #1

static/index.html

@@ -304,9 +304,9 @@ document.getElementById('fileInput').addEventListener('change', async function(e
     '</div>'
   ).join('');
 
-  // Scan all in parallel (limited to 4 at a time to avoid memory issues)
+  // Scan in small batches — iOS Safari can't handle many concurrent file reads
   const results = [];
-  const batchSize = 4;
+  const batchSize = 2;
   for (let i = 0; i < files.length; i += batchSize) {
     const batch = files.slice(i, i + batchSize);
     const batchResults = await Promise.all(batch.map(f => scanPhoto(f)));
@@ -321,12 +321,9 @@ document.getElementById('fileInput').addEventListener('change', async function(e
 async function scanPhoto(file) {
   const result = { file, exif: null, hasGps: false, lat: null, lng: null, thumb: null };
 
-  // Generate thumbnail
-  result.thumb = await new Promise(resolve => {
-    const reader = new FileReader();
-    reader.onload = e => resolve(e.target.result);
-    reader.readAsDataURL(file);
-  });
+  // Use object URL instead of readAsDataURL — avoids loading the entire file
+  // into memory as a base64 string (the main cause of iOS hangs with many photos)
+  result.thumb = URL.createObjectURL(file);
 
   // Read EXIF
   try {
@@ -726,6 +723,12 @@ async function pushGpsToAsset(idx) {
 }
 
 function resetAll() {
+  // Revoke all blob URLs to prevent memory leaks
+  allPhotos.forEach(p => {
+    if (p.thumb && p.thumb.startsWith('blob:')) {
+      URL.revokeObjectURL(p.thumb);
+    }
+  });
   allPhotos = [];
   selectedIdx = -1;
   currentFilter = 'all';