Integrity: Baseline a Directory with a SHA256SUMS Manifest

Baseline a directory for integrity monitoring. The data files live in /root/case/baseline (all *.dat). Both things you produce are regular files that you write with output redirection (>), not directories.

1. Write the SHA-256 of report.dat to the file /root/case/hash.txt. The bare 64-hex digest is what's asked for; the full line sha256sum prints for it (<digest> report.dat) is accepted too.

2. Write a manifest of every .dat file to the file /root/case/baseline/SHA256SUMS, in the format sha256sum itself prints: one <digest> <filename> line per file. That's the format sha256sum -c SHA256SUMS reads back to re-check integrity later, so run it to confirm every line says OK.

The file set varies per session. See /root/case/brief.txt.