add data-driven navigation with admin editor

Replace hardcoded header, footer and mobile nav with settings-driven
loops. Nav items stored as JSON via Settings, loaded in ThemeHook with
sensible defaults. New admin navigation editor at /admin/navigation
for add/remove/reorder/save/reset. Mobile bottom nav also driven from
header nav items with icon mapping by slug.

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

lib/berrypod_web/theme_hook.ex

@@ -17,6 +17,28 @@ defmodule BerrypodWeb.ThemeHook do
   alias Berrypod.{Products, Settings, Media}
   alias Berrypod.Theme.{CSSCache, CSSGenerator}
 
+  @default_header_nav [
+    %{"label" => "Home", "href" => "/", "slug" => "home"},
+    %{
+      "label" => "Shop",
+      "href" => "/collections/all",
+      "slug" => "collection",
+      "active_slugs" => ["collection", "pdp"]
+    },
+    %{"label" => "About", "href" => "/about", "slug" => "about"},
+    %{"label" => "Contact", "href" => "/contact", "slug" => "contact"}
+  ]
+
+  @default_footer_nav [
+    %{"label" => "Delivery & returns", "href" => "/delivery", "slug" => "delivery"},
+    %{"label" => "Privacy policy", "href" => "/privacy", "slug" => "privacy"},
+    %{"label" => "Terms of service", "href" => "/terms", "slug" => "terms"},
+    %{"label" => "Contact", "href" => "/contact", "slug" => "contact"}
+  ]
+
+  def default_header_nav, do: @default_header_nav
+  def default_footer_nav, do: @default_footer_nav
+
   def on_mount(:mount_theme, _params, _session, socket) do
     theme_settings = Settings.get_theme_settings()
 
@@ -43,6 +65,8 @@ defmodule BerrypodWeb.ThemeHook do
         :is_admin,
         !!(socket.assigns[:current_scope] && socket.assigns.current_scope.user)
       )
+      |> assign(:header_nav_items, load_nav("header_nav", @default_header_nav))
+      |> assign(:footer_nav_items, load_nav("footer_nav", @default_footer_nav))
 
     {:cont, socket}
   end
@@ -64,4 +88,11 @@ defmodule BerrypodWeb.ThemeHook do
         {:halt, Phoenix.LiveView.redirect(socket, to: "/coming-soon")}
     end
   end
+
+  defp load_nav(key, default) do
+    case Settings.get_setting(key) do
+      items when is_list(items) -> items
+      _ -> default
+    end
+  end
 end