POST /api/v1/import/roll20 accepts single or campaign exports (2 MiB
bound), maps through the importer onto the existing character storage
path so imports are owned by the caller and owner-scoped everywhere;
importer ValueErrors map to 422 with the fail-loud reason, all-
malformed campaigns refuse rather than fake a 200-with-zero. Foundry
preview route is a deliberate documented 501 — directory trees need
multipart support, pinned by test so it can't regress into fake
success. 7 red-first tests; suite at 406.
Co-Authored-By: Claude <[email protected]>
