Render a preview per bank question, client-side, from the source PDF cropped to
the question's bounds — makes the bank visually browsable like the spike cockpit.
bankCrops.ts: renders each template's PDF once (cached) via the existing pdf.js
loader (already at the 780px coordinate space the bounds live in), then crops the
page image to (bounds.x, bounds.y - pageTop, w, h) → a small PNG data-URL; decoded
page images are cached too. QuestionBankPage: a lazy <QuestionCrop> at the top of
each card (spinner → image, or "no preview" when a question has no bounds/PDF).
No API/infra change. tsc clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
