v31 — set_volume command for STREAM_ALARM

What's in v31

New `set_volume` kiosk_command. Sets the device's STREAM_ALARM volume — the loudness level used by `play_media` (and bypassed/overridden by the security siren). Companion to v30's `play_media` for alarm-clock automations.

Example: crank volume before wakeup, restore after

```yaml

• alias: Bedroom wakeup
  trigger:

  • platform: time
    at: "06:59:55"
    action:
  • event: kiosk_command
    event_data: { device: Bedroom Dashboard, command: set_volume, value: "0.8" }

• alias: Bedroom wakeup fire
  trigger:

  • platform: time
    at: "07:00:00"
    action:
  • event: kiosk_command
    event_data: { device: Bedroom Dashboard, command: play_media, value: "http://homeassistant.local:8123/local/wakeup.mp3" }

• alias: Bedroom dismiss
  trigger:

  • platform: state
    entity_id: input_button.bedroom_dismiss
    action:
  • event: kiosk_command
    event_data: { device: Bedroom Dashboard, command: stop_media }
  • event: kiosk_command
    event_data: { device: Bedroom Dashboard, command: set_volume, value: "0.3" }
    ```

What it doesn't affect

• Security siren — peg-to-max regardless of this setting
• Spotify Connect volume — separate path, controlled from phone Spotify slider or footer +/− buttons
• STREAM_MUSIC — not used by anything we control

For finer-grained control of those other paths, future commands like `set_media_volume` / `set_spotify_volume` would be obvious follow-ups.