Feature: Add photo management capabilities (list/count + delete action)

[MTrab]

Summary

Add HA support for robot photos (at minimum photo count sensor and delete action).

Why this matters

Useful, but lower priority than core speech/settings/actions.

SDK evidence (no wire-pod dependency)

• RPCs in external_interface.proto:
  • PhotosInfo
  • Photo
  • Thumbnail
  • DeletePhoto

Proposed HA design

• sensor.photo_count
• Services: vector.delete_photo, optionally vector.fetch_photo
• DISABLED by default

Acceptance criteria

• Photo count updates reliably.
• Delete action validates photo id and handles SDK errors.
• Tests for empty/non-empty and delete flows.