refactor: centralize API client and config caching

src/core/event-bus.js

@@ -0,0 +1,10 @@
+// 轻量事件总线，避免模块之间的直接耦合
+export function createEventBus() {
+    const target = new EventTarget();
+
+    const on = (type, listener) => target.addEventListener(type, listener);
+    const off = (type, listener) => target.removeEventListener(type, listener);
+    const emit = (type, detail = {}) => target.dispatchEvent(new CustomEvent(type, { detail }));
+
+    return { on, off, emit };
+}