Set SilenceUsage: true on every leaf command

[nathanjcochran]

Summary

• Every command with a RunE now sets SilenceUsage: true as a literal field on its cobra.Command, instead of setting cmd.SilenceUsage = true inline after argument validation.
• A bad flag or invalid argument now prints just the error, instead of the error followed by the full help/usage text — the error used to get buried at the top of a long usage dump (most of which is not actually relevant to the user's command), making it hard to spot.
• Updated the "Cobra Usage Display Pattern" section in CLAUDE.md to describe the new, simpler rule.