feat(cli)!: render native parse diagnostics

[zigai]

Parse failures expose argparse or Click messages with an [interfacy] prefix. Give both backends concise errors, spelling suggestions, and help for the command that failed.

• Show full parent help when a required subcommand is missing
• Configure diagnostic presentation with diagnostic_layout, independently of help layouts
• Let plugins change or render diagnostics through transform_diagnostic and render_diagnostic
• Keep embedded invoke() silent and expose failure details through UsageError.diagnostic

Breaking Changes

• Parse failures from Interfacy.run(), the interfacy command, and ArgumentParser use Interfacy messages instead of backend error strings and the [interfacy] prefix. Consumers matching the old text need updated expectations, including for str(UsageError)

Verification

• just coverage verifies unknown-command suggestions on both backends
• Under coverage run -m pytest, diagnostic hints identify the simulated script as tool
• Direct pytest verifies the same hints on Python 3.10, 3.14, 3.15
• The installed CLI omits private-input from the error for --unknown=private-input