License.vendor (free-text string) is now vendorId, a required FK to
Vendor, per docs/asset-license-management.md's "## Vendor (chốt
2026-08-02)" spec. Mirrors the Request.employeeId string->FK precedent:
Zod validates UUID format only, Prisma's own FK constraint (P2003) is
caught at insert time and translated into a clean 400 instead of a raw
500. No License data existed yet, so this is a pure column-type
migration, no backfill needed.
Also converts createLicense() to the {ok,value}|{ok,error} result
pattern used elsewhere (createRequest, createAssetItem) instead of
returning a bare LicenseRecord promise - closes the gap flagged in
CLAUDE.md now that License has its first FK-violation error case to
handle.
toanhoang