Add product search with autocomplete, filters, and sort

- Header: search button opening a command-palette dialog with debounced
  product suggestions, a term chip, and View All
- Command: shadcn-shaped primitives built on the project's own Dialog so
  no cmdk/radix dependency is introduced
- /search: results grid with item count, sort (relevance, price asc/desc),
  and cursor-based load more
- Filters: driven by the API's productFilters facets — colour swatches,
  labelled lists with counts, and a price range — round-tripped through
  each facet's raw input string so no filter shape is hardcoded

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jWbNNJLksC1QG8z8845FX

components/shopify/header.tsx

@@ -4,6 +4,7 @@ import React, { useState } from 'react';
 import Link from 'next/link';
 import { useCartStore } from '@/hooks/use-shopify-cart';
 import CartDrawer from '@/components/shopify/cart-drawer';
+import SearchDialog from '@/components/shopify/search-dialog';
 import { RiShoppingBagLine, RiCloseLine, RiMenu3Line } from '@remixicon/react';
 import { Button } from '@/components/ui/button';
 
@@ -86,6 +87,7 @@ const Header: React.FC<HeaderProps> = ({
 
           {/* Actions */}
           <div className="flex items-center gap-x-1">
+            <SearchDialog />
             <CartIcon />
 
             {/* Mobile hamburger */}