refactor(characters): drive shared UI from active character

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

@@ -1,6 +1,9 @@
 import { describe, expect, it } from "vitest";
 
-import { DEFAULT_CHARACTER_ID } from "@/data/constants/character";
+import {
+  DEFAULT_CHARACTER,
+  DEFAULT_CHARACTER_ID,
+} from "@/data/constants/character";
 import {
   ChatSendResponseSchema,
   type ChatSendResponse,
@@ -35,6 +38,7 @@ function makeResponse(
 function makeChatState(overrides: Partial<ChatState> = {}): ChatState {
   return {
     characterId: DEFAULT_CHARACTER_ID,
+    emptyChatGreeting: DEFAULT_CHARACTER.emptyChatGreeting,
     messages: [],
     promotion: null,
     outgoingMessageRevision: 0,