Add two grammar notes under new "Irregular Verbs" category: - Most Common Irregular Verbs: 15 essential verbs with present and preterite forms plus example sentences - Types of Irregular Verbs: spelling changes, stem changes, and unique irregulars with patterns and examples Closes #5 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>