Add unique_id to switch & button entities (UI-manageable, hideable)

[lebdim]

Summary

Docker container switch and button entities currently have no unique_id, so they never get an entity-registry entry. As a result they can't be hidden, renamed, assigned to an area, or exposed/hidden from the Wear OS and Android Auto companion apps (both filter on the entity registry). On installs with many containers this clutters those apps with restart buttons and on/off switches that can't be curated.

This adds a stable unique_id to both DockerContainerSwitch and DockerContainerButton:

{instance}_{container}_switch      # switch
{instance}_{container}_restart     # button

Why the entity_id setter is also needed

Both classes override entity_id with a read-only property. Once an entity has a unique_id, Home Assistant's entity platform registers it and then assigns entity.entity_id = entry.entity_id, which raises AttributeError on a read-only property and leaves the entity unavailable. Adding an entity_id setter fixes this.

Because the registry derives suggested_object_id from the entity's existing entity_id, existing entity_ids are preserved — no dashboards/automations break on upgrade (verified on a live install: 26 switches + 27 buttons re-registered with identical entity_ids, 0 renamed).

Changes

• switch.py: _attr_unique_id + entity_id setter on DockerContainerSwitch
• button.py: _attr_unique_id + entity_id setter on DockerContainerButton

Testing

Live install (HA 2026.7): after restart all switch/button entities register with a unique_id, are available with correct state, gain UI management (rename/area/hide/expose), and keep their original entity_ids. Sensors (already unique-id-less) are untouched.

[lebdim]

@ualex73 please check this too