Add notification command_screen_off

[markfrancisonly]

Proposed change

Documents the new command_screen_off notification command from home-assistant/android#7162, which turns the display off, aimed at wall-mounted dashboards; command_screen_on turns it back on. Only the display is affected: with the persistent connection set to always, the device keeps receiving commands while dark, so the server can turn the screen back on at any time.

Adds the command table row and a Screen Off section covering the two-step device admin activation, the secure lock screen refusal (the activation is never requested in that case), the persistent connection tip, and an example automation.

Type of change

• Document existing features within Home Assistant Companion App
• Document new or changing features for which there is an existing pull request elsewhere
• Spelling or grammatical corrections, or rewording for improved clarity
• Changes to the backend of this documentation
• Remove stale or deprecated documentation

Checklist

• I have read and followed the documentation guidelines.
• I have verified that my changes render correctly in the documentation.

Additional information

• Link to relevant existing code or pull request: Add command_screen_off to turn the display off while the device stays awake android#7162