add generic page renderer with block dispatch

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

test/berrypod/pages_test.exs

@@ -1,9 +1,15 @@
 defmodule Berrypod.PagesTest do
-  use Berrypod.DataCase, async: true
+  use Berrypod.DataCase, async: false
 
   alias Berrypod.Pages
   alias Berrypod.Pages.{Page, BlockTypes, Defaults, PageCache}
 
+  setup do
+    # Clear cached pages between tests so save_page side effects don't leak
+    PageCache.invalidate_all()
+    :ok
+  end
+
   describe "get_page/1" do
     test "returns defaults when nothing in DB" do
       page = Pages.get_page("home")