add FTS5 full-text product search

Adds SQLite FTS5 search index with BM25 ranking across product title,
category, variant attributes, and description. Search modal now has
live results with thumbnails, prices, and click-to-navigate. Index
rebuilds automatically after each provider sync.

Also fixes Access syntax on Product/ProductImage structs (Map.get
instead of bracket notation) which was causing crashes when real
products were loaded from the database.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/simpleshop_theme_web/live/shop/collection.ex

@@ -101,6 +101,8 @@ defmodule SimpleshopThemeWeb.Shop.Collection do
       cart_drawer_open={@cart_drawer_open}
       cart_status={assigns[:cart_status]}
       active_page="collection"
+      search_query={assigns[:search_query] || ""}
+      search_results={assigns[:search_results] || []}
     >
       <main id="main-content">
         <.collection_header

lib/simpleshop_theme_web/live/shop/product_show.ex

@@ -20,14 +20,14 @@ defmodule SimpleshopThemeWeb.Shop.ProductShow do
 
     # Build gallery images from local image_id or external URL
     gallery_images =
-      (product[:images] || [])
+      (Map.get(product, :images) || [])
       |> Enum.sort_by(& &1.position)
       |> Enum.map(fn img -> ProductImage.direct_url(img, 1200) end)
       |> Enum.reject(&is_nil/1)
 
     # Initialize variant selection
     option_types = Product.option_types(product)
-    variants = product[:variants] || []
+    variants = Map.get(product, :variants) || []
     {selected_options, selected_variant} = initialize_variant_selection(variants)
     available_options = compute_available_options(option_types, variants, selected_options)
     display_price = variant_price(selected_variant, product)