add newsletter and email campaigns

Subscribers with double opt-in confirmation, campaign composer with
draft/scheduled/sent lifecycle, admin dashboard with overview stats,
CSV export, and shop signup form wired into page builder blocks.

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

priv/repo/migrations/20260228204908_create_newsletter.exs

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+defmodule Berrypod.Repo.Migrations.CreateNewsletter do
+  use Ecto.Migration
+
+  def change do
+    create table(:newsletter_subscribers, primary_key: false) do
+      add :id, :binary_id, primary_key: true
+      add :email, :string, null: false
+      add :status, :string, null: false, default: "pending"
+      add :confirmation_token, :string
+      add :confirmed_at, :utc_datetime
+      add :unsubscribed_at, :utc_datetime
+      add :consent_text, :string
+      add :source, :string, default: "website"
+      add :ip_hash, :string
+
+      timestamps(type: :utc_datetime)
+    end
+
+    create unique_index(:newsletter_subscribers, [:email])
+    create index(:newsletter_subscribers, [:status])
+    create index(:newsletter_subscribers, [:confirmation_token])
+
+    create table(:newsletter_campaigns, primary_key: false) do
+      add :id, :binary_id, primary_key: true
+      add :subject, :string, null: false
+      add :body, :text, null: false
+      add :status, :string, null: false, default: "draft"
+      add :scheduled_at, :utc_datetime
+      add :sent_at, :utc_datetime
+      add :sent_count, :integer, default: 0
+      add :failed_count, :integer, default: 0
+
+      timestamps(type: :utc_datetime)
+    end
+
+    create index(:newsletter_campaigns, [:status])
+    create index(:newsletter_campaigns, [:scheduled_at])
+  end
+end