fix(scriptc): Capture the BMC USB service log to a file, not the console

journalctl now runs with -o short-iso into log/bmc_usb_net.log and is
copied into the job directory with the other monitor logs. rm -f first so
the file covers this run only, and the ISO timestamps line up with
mgmt_ping.log and nfc_poll.log for cross-referencing.

The cost, recorded rather than glossed over: it is no longer echoed to
the console, so the USB copy is the only copy. That cp return value is
not checked - the same shape as the nfc_polling.log filename bug, which
failed silently and was only noticed back at the desk with a job archive
missing a file.

Folded into V1.1.6 rather than bumping: the tag has not moved on and this
is the same delivery.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014RetWKFZFG1ZHcitQAyhwM

CLAUDE.md

@@ -239,6 +239,9 @@ Tera Term 連 COM port (115200-8-N-1)
 - ⚠️ **ICB/PDB 一律走 VI2C（`blanton_icb_vi2c.sh`），不要走 VSPI**：VSPI ~18 ms/reg 會讓 I2C
   byte 相間隔拉到 ~50 ms，踩中 SMBus 25–35 ms timeout，裝置直接 NACK。實測全掃 9.4 s vs 34.0 s。
 - ⚠️ **I2C 讀一律 Repeated START**（不是 STOP + START），否則 PMBus/SMBus 裝置（VRM、EFUSE）不理。
+- ⚠️ **Script C 的 BMC USB service log 不進 master log**：改成
+  `journalctl ... > log/bmc_usb_net.log` 再複製到隨身碟，**那是唯一一份**。
+  收工後翻不到就先確認 job 目錄裡有沒有這個檔
 - ⚠️ **VI2C 這條路的壞法是「只壞高位元組」**，不是整包壞掉。`11.98 V` 會變成 `32.00 V`
   —— 正的、數量級也不誇張，**擋全一/全零的過濾完全攔不到**。寫任何 VI2C 讀值工具都要有
   合理範圍檢查 + 重讀，光靠 `PDB_REJECT_FFFF` 那種是不夠的（`pwr_brick.sh` 的教訓）