v0.9.40
Added postal issuer and stamp variant foundations
Countries can now present related postal issuers and catalogue-recognized stamp variants through shared global structures.
Changes
- Added a shared postal issuer hierarchy with compact related-issuer browsing on country pages.
- Added independent collectible variant groups while preserving per-stamp collection, image, Theme, and Series behavior.
- Kept sheet, booklet, pane, and coil formats separate from collectible stamp variants.