Get device_id for assist if not set

[ADHDSquir]

This PR adds area awareness to Assist pipelines created by StreamAssist. If the device_id for Assist was not defined via a service call, the switch will pass the device_id of its parent service to Assist which is then used by assist to get the area. I have tested this with the standard Assist pipeline as well as with the Extended OpenAI Conversation integration.

When using Extended OpenAI Conversation, the prompt should include Current Area: {{ area_name(current_device_id) }} as described in that integration's docs.

Addresses #22 and #25