feat(bmc): Re-enable bmc_monitor with an I2C write/read-back test

bmc_monitor.sh comes back into the run with a second job beyond the
`free -m` sampling: an I2C pattern test against bus 1, address 0x41,
offset 0x00C0 -- write 55AA55AA and read it back, then write AA55AA55
and read that back. Two complementary patterns catch a stuck bit either
way round, and repeating it through the soak turns an intermittent I2C
fault into something the log shows rather than something the tester has
to catch live.

Script B starts it alongside the other stress; Script C stops it and
cats log/bmc_poll.log.

bmc_monitor_ddr.sh stays disabled -- BMC DDR stress runs through
bgctl + bmc-manager.

Docs: the "disabled" notes I added last time now applied to only half
the pair and read as wrong for bmc_monitor.sh. Split so the monitor is
documented as live with its I2C test, and only the _ddr variant is
marked disabled.

Script A -> V1.0.8.

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

CLAUDE.md

@@ -85,7 +85,8 @@ chmod +x ~/Blanton_Script/*.sh               # 佈署後必做一次
 ~/Blanton_Script/mgmt_ping_monitor.sh stop
 ~/Blanton_Script/mgmt_ping_monitor.sh summary  # 只看每段的 RESULT 行
 #   ⚠️ tail 子命令是 tail -f，會卡住不返回；TTL 裡要倒 log 請用 cat
-#   ⚠️ bmc_monitor.sh / bmc_monitor_ddr.sh 已停用（改走 bgctl + bmc-manager），檔案仍在
+#   bmc_monitor.sh   start/stop         # free -m + BMC I2C 寫入/讀回圖樣測試，log/bmc_poll.log
+#   ⚠️ bmc_monitor_ddr.sh 已停用（DDR 壓力改走 bgctl + bmc-manager），檔案仍在
 
 # ── 背景壓力（平台工具）──────────────────────────────
 bgctl run /usr/sbin/memtester 1G 100