add admin page editor with block reordering and management

Stage 6 of the page builder: admin UI at /admin/pages for managing
page layouts. Page list shows all 14 pages grouped by category.
Editor supports reorder (up/down), add, remove, duplicate, save,
and reset to defaults. DirtyGuard JS hook warns on unsaved changes.
ARIA live regions announce block operations for screen readers.

Also: regenerate admin icons (81 rules via mix task with @layer
wrapping), add gen_smtp dep for SMTP email adapter, add :key to
page renderer block loop for correct LiveView diffing.

1309 tests, 0 failures.

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

lib/berrypod_web/router.ex

@@ -229,6 +229,8 @@ defmodule BerrypodWeb.Router do
       live "/providers/:id/edit", Admin.Providers.Form, :edit
       live "/settings", Admin.Settings, :index
       live "/settings/email", Admin.EmailSettings, :index
+      live "/pages", Admin.Pages.Index, :index
+      live "/pages/:slug", Admin.Pages.Editor, :edit
       live "/redirects", Admin.Redirects, :index
     end