Replace fmt, errors, strings, encoding/json with Core primitives
across 20 files. Keep strings.Fields/CutPrefix. No translation
files modified.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Single-token generation validators for article correctness and irregular
verb form accuracy, leveraging the 1B model's 100% accuracy on both tasks.
Includes batch variants and 14 mock tests covering correct/wrong/empty/
context-cancellation/whitespace cases.
Co-Authored-By: Virgil <virgil@lethean.io>