feat: Expand Vocab with evals for other grades

[adnanrhussain]

Summary

Extends the Vocabulary Evaluator (notebook) to support additional grades, beyond the existing grades 3-4 support.

Key Changes

• Prompts: Expanded grade coverage from 3-4 to K-12 using two prompt sets (grades 3-4 use existing tested prompts; K-2, 5-12 use universal prompts with worked examples)
• Output Format: Ensured all grades return consistent complexity labels regardless of which prompt set is used
• Grade Routing: Added helper function to automatically select the correct prompts based on student grade level
• Testing: Added comprehensive test suite with multi-attempt validation

Testing

TODO

Status

🔄 Under internal review and testing before release.

Breaking Changes

None - backwards compatible.