Cover ChunkBbox construction and serialization, ChunkBboxResponse
camelCase output, rechunk endpoint bbox propagation, and frontend
store test data alignment with the new bboxes field.
Extract bounding boxes from chunk doc_items provenance in the chunker,
propagate through domain/service/API layers, and render highlighted
bboxes on canvas when hovering a chunk card. Reset highlights on
mode and page changes to prevent stale visual state.
Filter chunks by current PDF page for consistency with Verify mode.
Add collapsible chunking config section and paginated chunk list.
Show BboxOverlay in Prepare mode so users see element bounding boxes.
Fix scroll containment on prepare panel.
