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>

lib/berrypod_web/helpers/seo_helpers.ex

@@ -0,0 +1,107 @@
+defmodule BerrypodWeb.Helpers.SeoHelpers do
+  @moduledoc """
+  SEO-related helpers for generating structured data.
+  """
+
+  import Phoenix.Component, only: [assign: 3]
+  alias Berrypod.Media
+
+  @doc """
+  Generates FAQPage JSON-LD schema from page blocks.
+
+  Extracts FAQ items from any FAQ blocks on the page and builds a valid
+  FAQPage schema. Returns nil if no FAQ blocks with valid content are found.
+
+  ## Examples
+
+      iex> faq_json_ld([%{"type" => "faq", "settings" => %{"items" => [...]}}])
+      ~s({"@context":"https://schema.org","@type":"FAQPage",...})
+
+  """
+  def faq_json_ld(blocks) when is_list(blocks) do
+    questions =
+      blocks
+      |> Enum.filter(&(&1["type"] == "faq"))
+      |> Enum.flat_map(fn block ->
+        (block["settings"] || %{})["items"] || []
+      end)
+      |> Enum.filter(fn item ->
+        question = String.trim(item["question"] || "")
+        answer = String.trim(item["answer"] || "")
+        question != "" and answer != ""
+      end)
+      |> Enum.map(fn item ->
+        %{
+          "@type" => "Question",
+          "name" => item["question"],
+          "acceptedAnswer" => %{
+            "@type" => "Answer",
+            "text" => item["answer"]
+          }
+        }
+      end)
+
+    if questions != [] do
+      %{
+        "@context" => "https://schema.org",
+        "@type" => "FAQPage",
+        "mainEntity" => questions
+      }
+      |> Jason.encode!(escape: :html_safe)
+    else
+      nil
+    end
+  end
+
+  def faq_json_ld(_), do: nil
+
+  @doc """
+  Assigns an og_image URL to the socket based on page-specific or default image.
+
+  Priority: page-specific image > site-wide default > none
+  """
+  def assign_og_image(socket, page, base) do
+    og_image_id = get_og_image_id(page)
+
+    og_image =
+      cond do
+        og_image_id ->
+          Media.get_image(og_image_id)
+
+        true ->
+          Media.get_default_og_image()
+      end
+
+    if og_image do
+      url = og_image_url(og_image, base)
+      assign(socket, :og_image, url)
+    else
+      socket
+    end
+  end
+
+  defp get_og_image_id(nil), do: nil
+  defp get_og_image_id(%{og_image_id: id}), do: id
+  defp get_og_image_id(page) when is_map(page), do: page[:og_image_id]
+  defp get_og_image_id(_), do: nil
+
+  @doc """
+  Generates a full URL for an OG image, preferring 1200px width for social sharing.
+
+  Falls back to the largest available width if the image is smaller than 1200px.
+  """
+  def og_image_url(image, base) do
+    path =
+      if image.is_svg do
+        "/image_cache/#{image.id}.webp"
+      else
+        widths = Berrypod.Images.Optimizer.applicable_widths(image.source_width)
+        # Prefer 1200px or larger, otherwise use the largest available
+        width = Enum.find(widths, List.last(widths), &(&1 >= 1200))
+
+        "/image_cache/#{image.id}-#{width}.webp"
+      end
+
+    base <> path
+  end
+end