add admin dashboard with setup checklist and stats

Dashboard at /admin shows setup progress (when not live), stat cards
(orders, revenue, products), and recent paid orders table. Replaces
the old AdminController redirect. Add Dashboard to sidebar nav as
first item, update admin bar and theme editor links to /admin.

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

lib/simpleshop_theme_web/components/layouts.ex

@@ -46,6 +46,10 @@ defmodule SimpleshopThemeWeb.Layouts do
   end
 
   @doc false
+  def admin_nav_active?(current_path, "/admin") do
+    if current_path == "/admin", do: "active", else: nil
+  end
+
   def admin_nav_active?(current_path, link_path) do
     if String.starts_with?(current_path, link_path), do: "active", else: nil
   end

lib/simpleshop_theme_web/components/layouts/admin.html.heex

@@ -34,7 +34,7 @@
     <aside class="bg-base-200 w-64 min-h-full flex flex-col">
       <%!-- sidebar header --%>
       <div class="p-4 border-b border-base-300">
-        <.link navigate={~p"/admin/orders"} class="text-lg font-bold tracking-tight">
+        <.link navigate={~p"/admin"} class="text-lg font-bold tracking-tight">
           SimpleShop
         </.link>
         <p class="text-xs text-base-content/60 mt-0.5 truncate">
@@ -45,6 +45,14 @@
       <%!-- nav links --%>
       <nav class="flex-1 p-2" aria-label="Admin navigation">
         <ul class="menu gap-0.5">
+          <li>
+            <.link
+              navigate={~p"/admin"}
+              class={admin_nav_active?(@current_path, "/admin")}
+            >
+              <.icon name="hero-home" class="size-5" /> Dashboard
+            </.link>
+          </li>
           <li>
             <.link
               navigate={~p"/admin/orders"}

lib/simpleshop_theme_web/components/layouts/shop.html.heex

@@ -3,7 +3,7 @@
   style="background-color: var(--t-surface-raised, #f5f5f5); border-bottom: 1px solid var(--t-border-default, #e5e5e5); padding: 0.25rem 1rem; font-size: 0.75rem; text-align: right;"
 >
   <.link
-    href={~p"/admin/orders"}
+    href={~p"/admin"}
     style="color: var(--t-text-secondary, #666); text-decoration: none;"
   >
     Admin