fix: parse escaped device mapper names

[tianrking]

Summary

• decode device-mapper's doubled-hyphen escaping when displaying LVM volume-group and logical-volume paths
• retain non-mapper devices and malformed mapper names unchanged
• add Linux regression coverage for hyphens in both volume-group and logical-volume names

Root cause

The existing greedy regular expression split /dev/mapper/<vg>-<lv> at the wrong hyphen when an LVM name contained an escaped --. For example, vg-var--log was shown as /dev/vg-var-/log rather than /dev/vg/var-log.

Validation

• go test ./... on Windows (build validation)
• Linux cross-compiled test binary executed under WSL: TestResolveMapperDevice
• git diff --check

Fixes #329