add pagination across all admin and shop views

URL-based offset pagination with ?page=N for bookmarkable pages.
Admin views use push_patch, shop collection uses navigate links.
Responsive on mobile with horizontal-scroll tables and stacking
pagination controls. Includes dev seed script for testing.

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

lib/berrypod_web/page_renderer.ex

@@ -439,10 +439,19 @@ defmodule BerrypodWeb.PageRenderer do
   # ── Collection blocks ───────────────────────────────────────────
 
   defp render_block(%{block: %{"type" => "collection_header"}} = assigns) do
+    count =
+      if assigns[:pagination] do
+        assigns.pagination.total_count
+      else
+        length(assigns[:products] || [])
+      end
+
+    assigns = assign(assigns, :product_count, count)
+
     ~H"""
     <.collection_header
       title={assigns[:collection_title] || "All Products"}
-      product_count={length(assigns[:products] || [])}
+      product_count={@product_count}
     />
     """
   end
@@ -525,7 +534,15 @@ defmodule BerrypodWeb.PageRenderer do
 
   defp render_block(%{block: %{"type" => "product_grid"}} = assigns) do
     show_category = assigns[:current_category] in [nil, :sale]
-    assigns = assign(assigns, :show_category, show_category)
+    collection_slug = assigns[:collection_slug] || "all"
+    current_sort = assigns[:current_sort] || "featured"
+    sort_params = if current_sort != "featured", do: %{"sort" => current_sort}, else: %{}
+
+    assigns =
+      assigns
+      |> assign(:show_category, show_category)
+      |> assign(:collection_slug, collection_slug)
+      |> assign(:sort_params, sort_params)
 
     ~H"""
     <div class="page-container">
@@ -541,6 +558,13 @@ defmodule BerrypodWeb.PageRenderer do
         <% end %>
       </.product_grid>
 
+      <.shop_pagination
+        :if={assigns[:pagination] && assigns[:pagination].total_pages > 1}
+        page={assigns[:pagination]}
+        base_path={~p"/collections/#{@collection_slug}"}
+        params={@sort_params}
+      />
+
       <%= if (assigns[:products] || []) == [] do %>
         <div class="collection-empty">
           <p>No products found in this collection.</p>