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>