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/store/projectStore.ts

@@ -0,0 +1,27 @@
+import { create } from "zustand";
+
+interface ProjectState {
+  currentProjectId: string | null;
+  setCurrentProjectId: (id: string | null) => void;
+}
+
+const getInitialProjectId = () => {
+  if (typeof window === "undefined") {
+    return null;
+  }
+  return localStorage.getItem("active_project");
+};
+
+export const useProjectStore = create<ProjectState>((set) => ({
+  currentProjectId: getInitialProjectId(),
+  setCurrentProjectId: (id) => {
+    if (typeof window !== "undefined") {
+      if (id) {
+        localStorage.setItem("active_project", id);
+      } else {
+        localStorage.removeItem("active_project");
+      }
+    }
+    set({ currentProjectId: id });
+  },
+}));