Typo auto-correction for unknown flags

[toiroakr]

Summary

When a user provides an unknown flag (e.g., --verbos instead of --verbose), politty should suggest the closest matching known flag using string similarity (Levenshtein distance).

Motivation

This is a common UX improvement found in many CLI frameworks (e.g., @effect/cli, git). It reduces user frustration from typos and helps users discover correct flag names without consulting help text.

Currently, politty handles unknown flags based on the Zod schema's unknown keys mode (strict/strip/passthrough), but does not suggest corrections.

Proposed Behavior

$ mycli --verbos
error: Unknown flag '--verbos'. Did you mean '--verbose'?

• When an unknown flag is detected (in strict or strip mode), compute the Levenshtein distance between the unknown flag and all known flags
• If a close match is found (e.g., distance ≤ 2 or relative threshold), include a "Did you mean ...?" suggestion in the error/warning message
• Should work for both long flags (--flag) and short flags (-f)
• Multiple suggestions may be shown if several flags are similarly close

Implementation Notes

• The correction logic should integrate with the existing unknown flag handling in src/validator/error-formatter.ts (formatUnknownFlag / formatUnknownFlagWarning)
• Known flags can be extracted from the Zod schema via src/core/schema-extractor.ts
• A simple Levenshtein distance implementation is sufficient (no external dependency needed)