Add /tools on|off startup toggle

[fairusage]

Summary

• add /tools on|off to disable or re-enable startup auto-print
• persist the preference in ~/.pi/agent/settings.json under loadedTools.showOnStartup
• fail safely when an existing settings file is invalid instead of overwriting it

Verification

• bun run test
• bun run validate

[shaftoe]

Hey @fairusage thanks for the contribution.

Have you seen the latest release? Now it just shows a simple unintrusive summary line like the rest of other Pi information (ctrl+o) to expand.

I'm not happy with the summary content and want to make it more informative but I don't think suppressing it completely with a toggle is necessary.

What's the problem you want to solve?