cifs: REST protocols/cifs surface (services + shares + sessions + volume nas cifs ref)

[hartsock]

Goal

Mirror ONTAP's CIFS protocol REST surface so the same tooling can enable a CIFS
server, create SMB shares, and list sessions. Mock surface; the Samba-backed data
plane lands in the following sub-issues.

Scope (protocol-cifs feature; depends on #52)

• GET/POST/PATCH/DELETE /api/protocols/cifs/services/{svm.uuid}:
  { enabled, name, ad_domain | workgroup, security, ... }.
• GET/POST/PATCH/DELETE /api/protocols/cifs/shares:
  { name, path, acls[], properties[] }.
• GET /api/protocols/cifs/sessions (read-only active sessions; sourced from
  Samba once the data plane lands, empty until then).
• Volume nas block surfaces an optional CIFS share reference.

Dependencies

#52.

Acceptance

• netapp-ontap SDK can create a CIFS service + share and read them back; hermetic
  (no smbd yet).