Add temperature-aware MD1200 fan control

das_fanctl.sh reads drive temps via smartctl (falling back to the EMM
backplane sensors), interpolates a fan percentage, and re-sends _shutup
on a 5s keepalive so the shelf does not revert to full speed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

fan_speed_das.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=Fan Speed Script - izebra (Dell MD1200 DAS)
+
+[Service]
+User=root
+WorkingDirectory=/root/fan_speed/
+ExecStart=/root/fan_speed/das_fanctl.sh
+Restart=always
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target