Implemented a Zustand-based project_id store, expanded project selection/switching to persist project_id,

and centralized backend requests via api/apiFetch (including data provider updates) to inject X-Project-ID.

src/lib/api.ts

@@ -0,0 +1,18 @@
+import axios from "axios";
+import { config } from "@config/config";
+import { useProjectStore } from "@/store/projectStore";
+
+export const API_URL = process.env.NEXT_PUBLIC_API_URL || config.BACKEND_URL;
+
+export const api = axios.create({
+  baseURL: API_URL,
+});
+
+api.interceptors.request.use((request) => {
+  const projectId = useProjectStore.getState().currentProjectId;
+  if (projectId) {
+    request.headers = request.headers ?? {};
+    request.headers["X-Project-ID"] = projectId;
+  }
+  return request;
+});