feat(characters): support character-scoped conversations

src/stores/chat/__tests__/chat-helpers.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from "vitest";
 
+import { DEFAULT_CHARACTER_ID } from "@/data/constants/character";
 import { ChatSendResponse } from "@/data/dto/chat";
 import type { ChatState } from "@/stores/chat/chat-state";
 import {
@@ -29,6 +30,7 @@ function makeResponse(
 
 function makeChatState(overrides: Partial<ChatState> = {}): ChatState {
   return {
+    characterId: DEFAULT_CHARACTER_ID,
     messages: [],
     promotion: null,
     outgoingMessageRevision: 0,