fix(bmc): Give bmc_monitor_ddr its own log so the two can run together

Both scripts defaulted to LOG_NAME="bmc_poll.log", and PID_FILE is
derived from it, so the monitor and the DDR stress shared one log and
one pid file -- while the whole point of the split is to run them at
the same time.

The failure was quiet rather than loud: is_running greps the pid's
cmdline for its own SCRIPT_NAME, so the second script did not recognise
the first as running and started anyway. prepare_log_on_start then
truncated the log the first one was writing (START_LOG_MODE=new), both
raced on the pid file, and a later stop could only reap whichever wrote
it last, orphaning the other.

bmc_monitor_ddr.sh now uses bmc_ddr.log, which also moves its pid file
to bmc_ddr.pid. Both remain covered by the *.log ignore rule.

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

src/Script_ABC_Blanton/Blanton_Script/bmc_monitor_ddr.sh

@@ -69,7 +69,7 @@ LOG_STDERR=0
 
 # Logging
 LOG_DIR=""                      # empty = <script directory>/log
-LOG_NAME="bmc_poll.log"
+LOG_NAME="bmc_ddr.log"
 MAX_LOG_SIZE_MB=100             # rotate above this size; 0 = never rotate
 MAX_LOG_KEEP=5                  # keep .1 .. .N