Fix: Use download_with_sanity_check() and fail container on download failure

backend/app/main.py

@@ -62,14 +62,14 @@ async def run_initial_download():
             logger.info(f"MTGJSON data already exists (last refresh: {last_refresh})")
             return
         
-        logger.info("Running initial MTGJSON data download...")
+        logger.info("Running initial MTGJSON data download with sanity checks...")
         logger.info("This may take several minutes depending on network speed...")
         
-        # Download files
-        success = await manager.download_files()
+        # Download files with sanity checking and retry logic
+        success = await manager.download_with_sanity_check()
         if not success:
-            logger.error("Failed to download MTGJSON files")
-            return
+            logger.error("Failed to download MTGJSON files after retries - marking container unhealthy")
+            raise RuntimeError("MTGJSON data download failed after all retry attempts")
         
         # Unpack files
         await manager.unpack_files()