- library: CRUD with root-path resolution (absolute, symlink-free, must be
readable). A library name is unique; the root is validated at creation.
- registry: media types declare their extensions; the core never imports a
module. RegisterType is the extension point.
- scanner: walks a root, reconciles media_items/media_files in one
transaction, skips unchanged files by size+mtime, and marks vanished files
missing rather than deleting them (progress is the one thing here that
cannot be regenerated). A single unreadable file never fails a scan.
- migration 0002: `missing` flags on items and files, plus indexes.
- endpoints: media-types, library list/get/create/delete, per-library items,
and scan. Library reads go through the same grant chokepoint as everything
else; an unauthorised library 404s rather than 403s so its existence is not
leaked.
