Fix HEIC thumbnails: pull full file + convert to JPEG via sips

HEIC is not front-loaded — partial 512KB reads produce broken output.
batch-thumbs now pulls full file for HEIC/HEIF, partial for JPEG/PNG.

sips: add --setProperty format jpeg to all thumbnail conversions so
HEIC files are always converted to JPEG. SkiaImage on JVM desktop
cannot decode HEIC natively — JPEG is required.

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

@@ -162,6 +162,9 @@ async def cmd_batch_thumbs(pairs_json: str):
     Pull thumbnails for multiple files in a single AFC session.
     Input: JSON array of [device_path, local_path] pairs.
     Output: JSON array of {devicePath, ok} results.
+    
+    For HEIC/HEIF files: pulls full file (partial read produces broken output).
+    For JPEG/PNG: reads first 512KB (enough for thumbnail extraction).
     """
     try:
         pairs = json.loads(pairs_json)
@@ -169,16 +172,21 @@ async def cmd_batch_thumbs(pairs_json: str):
         afc = await get_afc(lockdown)
         results = []
         for device_path, local_path in pairs:
+            ext = device_path.rsplit('.', 1)[-1].lower() if '.' in device_path else ''
+            is_heic = ext in ('heic', 'heif')
             try:
                 os.makedirs(os.path.dirname(os.path.abspath(local_path)), exist_ok=True)
-                try:
-                    data = await afc.fread(device_path, 512 * 1024, 0)
-                except Exception:
+                if is_heic:
+                    # HEIC: must pull full file — partial reads produce broken output
                     await afc.pull(device_path, local_path)
-                    results.append({'devicePath': device_path, 'ok': True})
-                    continue
-                with open(local_path, 'wb') as f:
-                    f.write(data)
+                else:
+                    # JPEG/PNG: 512KB partial read is sufficient
+                    try:
+                        data = await afc.fread(device_path, 512 * 1024, 0)
+                        with open(local_path, 'wb') as f:
+                            f.write(data)
+                    except Exception:
+                        await afc.pull(device_path, local_path)
                 results.append({'devicePath': device_path, 'ok': True})
             except Exception as e:
                 results.append({'devicePath': device_path, 'ok': False, 'error': str(e)})