fix(sync): clean old JSON files before downloading new orders

Previous sync runs left JSON files in the output directory, causing
order_reader to accumulate orders from multiple downloads instead of
only processing the latest batch.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/services/gomag_client.py

@@ -47,6 +47,13 @@ async def download_orders(
     out_dir = Path(json_dir)
     out_dir.mkdir(parents=True, exist_ok=True)
 
+    # Clean old JSON files before downloading new ones
+    old_files = list(out_dir.glob("gomag_orders*.json"))
+    if old_files:
+        for f in old_files:
+            f.unlink()
+        _log(f"Șterse {len(old_files)} fișiere JSON vechi")
+
     headers = {
         "Apikey": effective_key,
         "ApiShop": effective_shop,