Path() builds OS-aware absolute paths using Env("DS") — single point
of responsibility for filesystem paths. Relative paths anchor to
DIR_HOME. cleanPath resolves .. and double separators.
Env() now falls through to os.Getenv for unknown keys — universal
replacement for os.Getenv. Core keys (OS, DIR_HOME, etc.) take
precedence, arbitrary env vars pass through.
New exports: Path, PathBase, PathDir, PathExt, PathIsAbs, PathGlob,
CleanPath. Info init moved to init() so Path() can be used during
population without init cycle. DIR_HOME respects CORE_HOME env var
override for agent workspace sandboxing.
13 path tests, 17 env tests — all passing.
Co-Authored-By: Virgil <virgil@lethean.io>