6 catalog data and mode mappers (#25)

* supabase product proxy and rendering

* minor pipeline refactor

* refactoring and demand estimation

* trackion of date index searching

* fixing changes of imports

* data seeding

* chore: airline basic refactor

* feat: huge push of product changes and item review with cart

* refactored design

* chore: moving route elsewhere and align

* fix: build of web/

* chore: fixing paper build

* fixing chars

web/src/contexts/CartContext.tsx

@@ -0,0 +1,76 @@
+'use client';
+
+import { createContext, useContext, useState, useEffect, ReactNode } from 'react';
+
+export interface CartItem {
+  id: string;
+  type: 'hotel' | 'airline';
+  name: string;
+  price: number;
+  metadata: Record<string, unknown>;
+  dateIndex: number;
+}
+
+interface CartContextType {
+  items: CartItem[];
+  addItem: (item: CartItem) => void;
+  removeItem: (id: string) => void;
+  clearCart: () => void;
+  itemCount: number;
+}
+
+const CartContext = createContext<CartContextType | undefined>(undefined);
+
+const CART_KEY = 'phantom_cart';
+
+export const CartProvider = ({ children }: { children: ReactNode }) => {
+  const [items, setItems] = useState<CartItem[]>([]);
+  const [loaded, setLoaded] = useState(false);
+
+  // load cart from sessionStorage on mount
+  useEffect(() => {
+    const stored = sessionStorage.getItem(CART_KEY);
+    if (stored) {
+      try {
+        setItems(JSON.parse(stored));
+      } catch (e) {
+        console.error('[CART_LOAD]', e);
+      }
+    }
+    setLoaded(true);
+  }, []);
+
+  // persist to sessionStorage whenever cart changes
+  useEffect(() => {
+    if (!loaded) return;
+    sessionStorage.setItem(CART_KEY, JSON.stringify(items));
+  }, [items, loaded]);
+
+  const addItem = (item: CartItem) => {
+    setItems(prev => {
+      // prevent duplicates
+      if (prev.find(i => i.id === item.id)) return prev;
+      return [...prev, item];
+    });
+  };
+
+  const removeItem = (id: string) => {
+    setItems(prev => prev.filter(i => i.id !== id));
+  };
+
+  const clearCart = () => {
+    setItems([]);
+  };
+
+  return (
+    <CartContext.Provider value={{ items, addItem, removeItem, clearCart, itemCount: items.length }}>
+      {children}
+    </CartContext.Provider>
+  );
+};
+
+export const useCart = () => {
+  const ctx = useContext(CartContext);
+  if (!ctx) throw new Error('useCart must be used within CartProvider');
+  return ctx;
+};