Embed compact shapes in page entries for library exports, add geometry
verification and structure tests for backend, and remove the redundant
:format field from the manifest — version alone determines format.
AI-assisted-by: deepseek-v4-pro
Add feature-flagged compact export format where pages embed shapes
as a single JSON entry instead of one ZIP entry per shape. Shapes
go through compact-shape (prune defaults/nils/identity transforms)
and round-values (round floats to 4 decimals) before encoding.
Export: one JSON per page with embedded objects, manifest v2,
no pretty-printing. Gated by :binfile-v3-compact flag (opt-in).
Import: detect manifest version 2, expand compact shapes
(restore transforms, recompute selrect/points) on read.
AI-assisted-by: deepseek-v4-pro
