feat: add /host-sys volume mount and HOST_SYS_PATH environment variable for sysfs serial fallback and SMART health detection

Add HOST_SYS_PATH=/host-sys to .env.example and app.py config with /host-sys default. Update _device_serial() to check HOST_SYS_PATH/class/block and HOST_SYS_PATH/block before fallback /sys paths for serial reads. Update raid_status() SMART regex to match both "SMART overall-health self-assessment test result" and "SMART Health Status" with case-insensitive flag for NVMe/SSD compatibility. Add /

.env.example

@@ -37,4 +37,5 @@ RAID_DEVICE=/dev/md127
 STORAGE_CACHE_SECONDS=900
 # Optional: SMART-Abfragen aktivieren (benötigt Zugriff auf Host-Devices)
 SMART_ENABLED=false
+HOST_SYS_PATH=/host-sys
 LOG_LEVEL=INFO