feat: add file-based logging with hourly rotation and configurable retention period

Add LOG_FILE and LOG_RETENTION_HOURS environment variables to .env.example with defaults /data/media-max.log and 6 hours. Install TimedRotatingFileHandler with hourly rotation, 1 backup, UTF-8 encoding, and UTC timestamps. Add OSError exception handling with warning log when file logging unavailable. Add warn_on_nonzero parameter to _read_command() with default True and disable for smartctl -H calls to suppress expected

.env.example

@@ -38,4 +38,6 @@ STORAGE_CACHE_SECONDS=900
 # Optional: SMART-Abfragen aktivieren (benötigt Zugriff auf Host-Devices)
 SMART_ENABLED=false
 HOST_SYS_PATH=/host-sys
+LOG_FILE=/data/media-max.log
+LOG_RETENTION_HOURS=6
 LOG_LEVEL=INFO