CVE-2026-71458: Observable Response Discrepancy

URLModificationMiddleware resolves named-URL lookups against unfiltered Model.objects before RBAC. The 403→404 shim only rewrites 403 responses, leaving the pk=0 miss path with a different 404 detail string. Differential "Not found." vs "No <Model> matches..." reveals whether a named resource (org, credential, inventory, host) exists anywhere on the platform. Enables cross-tenant internal hostname enumeration.