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

docs/release-notes/v1.1.6.md

@@ -33,6 +33,10 @@
 * `comboA` / `comboB` for CB and each SWB CONN. `comboB` is `comboA` with every direction flipped, so running both covers each rail high and low while its neighbours sit the other way.
 * NC channels stay at `nominal` in both — there is nothing to margin on an unused rail (CONN14 CH10/11/13, CONN15 CH10).
 
+**The BMC USB service log is captured again — to a file**
+* Script C's `journalctl` dump had been commented out, so that service log reached nothing at all. It now runs with `-o short-iso` into `log/bmc_usb_net.log` and is copied into the job directory for the USB archive. The ISO timestamps line up with the other monitor logs, and `rm -f` first keeps the file to one run.
+* **It is no longer printed to the console**, so the USB copy is the only copy. If that `cp` fails — and nothing checks it — the service log is gone. Check the job directory before packing up.
+
 ## 📦 Downloads
 
 | File | Contents |
@@ -51,6 +55,7 @@ grep -rlU $'\r' ~/Blanton_Script    # expect no output
 ## ⚠️ Before you run
 
 * **`READ_VIN` and `READ_IIN` are not in the datasheet's coefficient table.** They are decoded here with the voltage and current coefficients — consistent with a ~50 V input, but not stated by the datasheet. Anything quoting brick Vin should have that confirmed first. `PB_VIN_M` / `PB_IIN_M` are where to change it.
+* **The BMC USB service log only exists on the USB stick.** It is not in the master console log any more.
 * **`NA` has two meanings**: nothing readable, or read but outside its plausibility window. Use `PB_TRIES=1 ./Blanton_Script/pwr_brick.sh show -r` to see the unretried raw words and tell them apart.
 * **Margin profiles are positional.** `comboA_SWB_CONN13` applied to a CONN16 board margins the wrong rails and nothing detects it.
 * **`blanton_multiphase_margin.sh save` is permanent**, and it must not be mixed with `margin.sh` — same rails, two access paths, no interlock.