Prepare CSV Preflight CLI for npm

[softpeanut]

Prepares the existing dependency-free CLI as the unscoped public csv-preflight package. The tarball is limited to the CLI, README, license, and package metadata.

The installed-package smoke exposed an existing delimiter bug: semicolon input was normalized as comma-separated output. This change preserves the detected delimiter and adds a regression test at the CLI boundary.

Verification:

• npm test — 30 passed
• npm pack --dry-run --json --ignore-scripts — four expected files, 7.2 kB
• Installed the packed tarball into a clean temporary prefix and ran its generated executable against the semicolon fixture; exit 1 and both output artifacts matched the documented issue contract

Publication is intentionally not claimed: npm authentication and 2FA are still required.