Fix SCSI detection on distros without sg module
Problem: On CachyOS, Arch, and other distros that don't load the sg kernel module by default, SCSI USB devices (like the Elite Vision 360) get /dev/sdb but no /dev/sg* — causing detection to silently fail.
Fix (two-pronged):
- Block device fallback: Detector now scans
/dev/sd*block devices when no/dev/sg*found — SG_IO ioctl works on both trcc setup-udevnow writes/etc/modules-load.d/trcc-sg.confand runsmodprobe sgimmediately
Addresses #46. 2516 tests.