Per-project Files — the hub's native attachments surface (P2b),
folder-scoped via PhoenixKitProjects.Attachments (core Storage; no
module table). Upload/browse rides core's MediaSelectorModal scoped to
the project folder; picked/uploaded files link into it, removal follows
the sole-home-soft-trash convention.
Gated on the built-in files extension (toggleable per project in the
Modules panel) + Authz.can?(…, :upload_files) for mutations; viewing
requires :view. Embeddable like every LV here.