fix(storage): use /host-dev for block device access inside container

Docker always creates a fresh tmpfs at /dev, silently dropping any
/dev:/dev bind mount. Block devices must be accessed via /host-dev
where the host /dev is actually mounted.

Changes:
- docker-compose.yml: /dev:/dev → /dev:/host-dev:rw
- safety.go: add HostDevPath constant + HostDevicePath() helper
- format_linux.go: all device ops (stat, sfdisk, partprobe, mkfs.ext4,
  blkid) use HostDevicePath() to resolve /dev/sdb → /host-dev/sdb
- safety_linux.go: IsSystemDisk() stats device via /host-dev
- scan_linux.go: enrichWithBlkid() probes each partition individually
  via /host-dev/sdXN instead of batch blkid -o export (which can't
  find devices when /dev is Docker's minimal tmpfs)

Fixes "stat /dev/sdb: no such file or directory" in FormatAndMount.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

controller/docker-compose.yml

@@ -30,8 +30,8 @@ services:
       - /etc/os-release:/host/etc/os-release:ro
       # Host hostname — for monitoring page (os.Hostname() returns container ID)
       - /etc/hostname:/host/etc/hostname:ro
-      # Block devices — required for storage init (lsblk, mkfs, sfdisk)
-      - /dev:/dev
+      # Block devices — mounted at /host-dev (can't override Docker's /dev tmpfs)
+      - /dev:/host-dev:rw
       # Host fstab — UUID-based mount persistence (mounted as /host-fstab inside container)
       - /etc/fstab:/host-fstab
       # udev metadata — for blkid/lsblk device model info