Shared filesystem path helpers for DeepSeek Harness user data.
## DSH home
`DSH_HOME_DIR_NAME` owns the default user-data directory name: `.dsh`.
`defaultDshHome()` returns the default DeepSeek Harness home by joining the operating-system home directory with `.dsh`, using Node's platform path rules.
`expandHomePath()` expands `~`, `~/...`, and Windows-style `~\...` prefixes against the operating-system home directory. It leaves non-tilde paths and `~user/...` untouched.
This package is intentionally small and harness-dep-free so product packages can share user-data path conventions without depending on one another.
- **Expansion is deliberately narrow** — only bare `~`, `~/...`, and `~\...` use the current operating-system home; named-user forms such as `~alice/...`, environment variables, and shell expressions remain unchanged.
- **Helpers do not touch the filesystem** — callers still own directory creation, existence checks, permissions, and trust policy for the resulting path.
