fix(provision): write-flash → write_flash for esptool v5 compat

esptool v5+ rejects hyphenated subcommands. The provision script
used 'write-flash' which fails with "invalid choice". Changed to
'write_flash' (underscore) which works with both old and new esptool.

Co-Authored-By: Ruflo & AQE

firmware/esp32-csi-node/provision.py

@@ -155,7 +155,7 @@ def flash_nvs(port, baud, nvs_bin):
             "--chip", "esp32s3",
             "--port", port,
             "--baud", str(baud),
-            "write-flash",
+            "write_flash",
             hex(NVS_PARTITION_OFFSET), bin_path,
         ]
         print(f"Flashing NVS partition ({len(nvs_bin)} bytes) to {port}...")