validateRelPath was checking strings.Contains(clean, "..") but
filepath.Clean("foo/../bar") = "bar" and Clean("../foo") = "..".
Update validateRelPath to check cleaned path for traversal patterns:
- contains "/../" (embedded ..)
- ends with "/.." (trailing ..)
- equals ".." (bare ..)
Also fix container_files_test.go test case "path ends in .." to
expect NO error (Clean("foo/..") = "foo" is a no-op normalise).
Add comment clarifying why substring checks are needed after Clean().
Add test case for Windows absolute path (C:\...) which Go on Linux
treats as a relative path — keep wantErr=true to catch on Windows CI.
Molecule AI Core-BE
e49179aa47