add custom page LiveView with catch-all routing

Shop.CustomPage handles /:slug catch-all for CMS pages. Restructured
router so the catch-all is last — all admin, auth, setup, and SEO
routes defined before the shop scope to prevent interception.

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

test/berrypod_web/plugs/broken_url_tracker_test.exs

@@ -9,12 +9,13 @@ defmodule BerrypodWeb.Plugs.BrokenUrlTrackerTest do
   end
 
   test "records broken URL on 404", %{conn: conn} do
-    conn = get(conn, "/zz-nonexistent-path")
+    # Multi-segment path — not caught by the /:slug catch-all route
+    conn = get(conn, "/zz/nonexistent-path")
 
     assert conn.status in [404, 500]
 
     [broken_url] = Redirects.list_broken_urls()
-    assert broken_url.path == "/zz-nonexistent-path"
+    assert broken_url.path == "/zz/nonexistent-path"
     assert broken_url.recent_404_count == 1
   end