fix: align [private] registry tag in dbc search output

[zeroshade]

Summary

Fixes #341.

• Renders the [private] registry tag as its own table column (between name and description) so it aligns consistently across drivers with different name lengths
• The extra column is only added when at least one driver has a registry tag, so output for public-only results is unchanged
• Adds a test asserting both [private] tags appear at the same column offset
• Updates docs examples to reflect the new alignment