feat(social): show friend presence and require online listening

api/openapi.yaml

@@ -2357,12 +2357,15 @@ components:
         playlist_name: {type: string}
     SocialPerson:
       type: object
-      required: [id, username, display_name, relationship, unread]
+      required: [id, username, display_name, relationship, unread, online]
       properties:
         id: {type: string, format: uuid}
         username: {type: string}
         display_name: {type: string}
         relationship: {type: string, enum: [none, incoming, outgoing, friend, blocked]}
+        online:
+          type: boolean
+          description: A current friend has an active client heartbeat within 45 seconds. Independent of music visibility; false for non-friends and blocked people.
         unread: {type: integer}
         activity: {$ref: '#/components/schemas/ListeningActivity'}
         last_message: {$ref: '#/components/schemas/SocialMessagePreview'}