add key command group, update provisioning

[crimeminister]

This pull request transitions the FOKS documentation from using the legacy foks device command group to the new, more general foks key command group. It also updates related documentation references, documents the new foks team inbox admin command, and removes obsolete ping command details.

• Replaces foks device with foks key group
  • Deleted cli/device.mdx
  • Created cli/key.mdx
  • Documented core key management commands: list, switch, lock, new, remove, and revoke.
  • Documented the new device provisioning commands under foks key device (specifically provision and make-permanent).
  • Documented shortcut synonyms such as foks key use-backup, foks key use-bot-token, and foks key use-yubikey.
• Updated references & navigation
  • Replaced cli/device with cli/key in docs.json.
  • Updated hyperlinks referencing the device page to point to the new key/device section in:
    • cli/bot.mdx
    • quickstart.mdx
  • Updated the main commands index table in cli/overview.mdx to reflect the foks key group instead of foks device
• Removed docs for (obsolete?) foks ping command
• Added docs for foks team inbox <team> command in cli/team.mdx
• Added AGENTS.md to .mintignore to prevent it from being build/deployed

[crimeminister]

@maxtaco Here's an attempt to freshen some docs to reflect the shape of the CLI that I discovered when setting up a foks instance. Please let me know if this is useful and/or if any changes are required.