add SEO enhancements: OG images, meta robots, FAQ block, image sitemap

- Per-page SEO controls: meta robots directives, focus keyword, OG image
- Site-wide default OG image in admin settings
- FAQ block type with FAQPage JSON-LD schema
- Enhanced Organization JSON-LD with business info, contact, address
- Image sitemap with product images
- SEO preview panel with Google/social card mockups
- SEO checklist with real-time scoring
- Business info section in site editor
- GSC integration scaffolding (OAuth, client, cache)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

priv/repo/migrations/20260417122216_add_seo_fields_to_pages.exs

@@ -0,0 +1,10 @@
+defmodule Berrypod.Repo.Migrations.AddSeoFieldsToPages do
+  use Ecto.Migration
+
+  def change do
+    alter table(:pages) do
+      add :meta_robots, :string, default: "index, follow"
+      add :focus_keyword, :string
+    end
+  end
+end