chore: 切换到 bun publish，修复 husky 路径问题，调整 diff 折叠距离，导出 VoiceContext

- publish-npm.yml: npm publish → bun publish，移除 setup-node，使用 BUN_CONFIG_TOKEN
- package.json: prepare 脚本 husky → bunx husky，版本 2.4.4 → 2.4.5
- Messages.tsx: DIFF_COLLAPSE_DISTANCE 从 0 改为 3，避免 diff 过度折叠
- voice.tsx: 导出 VoiceContext

src/context/voice.tsx

@@ -19,7 +19,7 @@ const DEFAULT_STATE: VoiceState = {
 
 type VoiceStore = Store<VoiceState>;
 
-const VoiceContext = createContext<VoiceStore | null>(null);
+export const VoiceContext = createContext<VoiceStore | null>(null);
 
 type Props = {
   children: React.ReactNode;