0b9e8bfe23
Records the design for issue #691 (make usernames case-insensitive): silently lowercase on ingest, explicit `oxicloud migrate lowercase-usernames [--dry-run]`, refuse-to-boot until DB is fully lowercase. Includes the chunked-upload directory rename step and the OIDC JIT lowercase fix surfaced during the design sweep. Design deferred pieces (display_name split, WebDAV URL redesign) are listed under "Not in scope" so the boundary is explicit. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>