Extends 72 for the locked S4-9 shape taxonomy (no Band/span):
- exam_questions: add bounds jsonb + page int (the drawn Part box; null for
derived main questions).
- exam_response_areas: add context_type (v1 generic, future STEM differentiation);
extend kind CHECK to response|context|question_number|mark_area|reference|furniture.
Additive + idempotent. Applied to dev .94 and verified (columns present; CHECK
def lists all 6 kinds). NOT applied to prod .156.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
