Feature: Add face enrollment management services

[MTrab]

Summary

Add services for enrolled face management (list, add/enroll, rename, delete).

Why this matters

Valuable for identity-aware robot experiences, but lower core automation value.

SDK evidence (no wire-pod dependency)

• RPCs in external_interface.proto:
  • RequestEnrolledNames
  • UpdateEnrolledFaceByID
  • EraseEnrolledFaceByID
  • SetFaceToEnroll / EnrollFace (if needed)
• AppIntent may also be used for meet/introduction flows.

Proposed HA design

• Services:
  • vector.add_face
  • vector.rename_face
  • vector.delete_face
  • vector.list_faces

Acceptance criteria

• Explicit service schemas for ids/names.
• Actionable errors for invalid ids/name conflicts.
• Tests for success + expected failures.