Refactor store context and improve responsiveness across the application

Refactored the `useStore` hook to be imported from a dedicated `StoreContext` to improve code organization and maintainability. Also, enhanced responsive design for better usability on various screen sizes, including tablet-specific adjustments for the sidebar and header.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 95e8aab4-f39f-4b48-aa57-a759ec15ba3d
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/1957c339-2757-4d1f-8e92-e9f71a1ce58e/95e8aab4-f39f-4b48-aa57-a759ec15ba3d/A90CXrX

client/src/contexts/StoreContext.tsx

@@ -0,0 +1,32 @@
+import { ReactNode, createContext, useContext } from "react";
+import type { Group } from "@shared/schema";
+
+interface StoreContextType {
+  selectedStoreId: number | null;
+  setSelectedStoreId: (storeId: number | null) => void;
+  stores: Group[];
+  sidebarCollapsed: boolean;
+  setSidebarCollapsed: (collapsed: boolean) => void;
+  mobileMenuOpen: boolean;
+  setMobileMenuOpen: (open: boolean) => void;
+  storeInitialized: boolean;
+}
+
+const StoreContext = createContext<StoreContextType | undefined>(undefined);
+
+export const useStore = () => {
+  const context = useContext(StoreContext);
+  if (!context) {
+    throw new Error("useStore must be used within a StoreProvider");
+  }
+  return context;
+};
+
+interface StoreProviderProps {
+  children: ReactNode;
+  value: StoreContextType;
+}
+
+export function StoreProvider({ children, value }: StoreProviderProps) {
+  return <StoreContext.Provider value={value}>{children}</StoreContext.Provider>;
+}