iOS thumbnails: use partial 512KB read for faster thumbnail generation

Add pull-thumb command to helper script that uses afc.fread() to read
only the first 512KB of each photo. EXIF thumbnails are in the first
few KB so sips can generate a resized thumbnail from the partial file.
Falls back to full afc.pull() if fread is unavailable.

IosConnector.pullToFile() uses pull-thumb for thumbnail requests.
Full afc.pull() still used for actual photo import.

src/main/resources/scripts/photophetch-ios-helper.py

@@ -135,6 +135,28 @@ async def cmd_pull(device_path: str, local_path: str):
         sys.exit(1)
 
 
+async def cmd_pull_thumb(device_path: str, local_path: str):
+    """Pull first 512KB — enough for EXIF thumbnail extraction via sips."""
+    try:
+        lockdown = await get_lockdown()
+        afc = await get_afc(lockdown)
+        os.makedirs(os.path.dirname(os.path.abspath(local_path)), exist_ok=True)
+        try:
+            # fread(path, size, offset) reads partial file — much faster than full pull
+            data = await afc.fread(device_path, 512 * 1024, 0)
+        except Exception:
+            # fread may not exist or may fail — fall back to full pull
+            await afc.pull(device_path, local_path)
+            print(json.dumps({'ok': True, 'path': local_path}))
+            return
+        with open(local_path, 'wb') as f:
+            f.write(data)
+        print(json.dumps({'ok': True, 'path': local_path}))
+    except Exception as e:
+        print(f'Error: {e}', file=sys.stderr)
+        sys.exit(1)
+
+
 async def cmd_delete(device_path: str):
     try:
         lockdown = await get_lockdown()
@@ -159,6 +181,8 @@ if __name__ == '__main__':
         asyncio.run(cmd_list_photos())
     elif command == 'pull' and len(sys.argv) == 4:
         asyncio.run(cmd_pull(sys.argv[2], sys.argv[3]))
+    elif command == 'pull-thumb' and len(sys.argv) == 4:
+        asyncio.run(cmd_pull_thumb(sys.argv[2], sys.argv[3]))
     elif command == 'delete' and len(sys.argv) == 3:
         asyncio.run(cmd_delete(sys.argv[2]))
     else: