Add "data export" feature

- Adds a button in Account Settings where you can request a ZIP export of your
  Fizzy data
- Export files are created in the background. When ready, a link to
  download them is sent to the requester.
- Exports expire after 24 hours. And are limited to 10 per day.

test/models/account/export_test.rb

@@ -0,0 +1,95 @@
+require "test_helper"
+
+class Account::ExportTest < ActiveSupport::TestCase
+  test "build_later enqueues ExportAccountDataJob" do
+    export = Account::Export.create!(account: Current.account, user: users(:david))
+
+    assert_enqueued_with(job: ExportAccountDataJob, args: [ export ]) do
+      export.build_later
+    end
+  end
+
+  test "build generates zip with card JSON files" do
+    export = Account::Export.create!(account: Current.account, user: users(:david))
+
+    export.build
+
+    assert export.completed?
+    assert export.file.attached?
+    assert_equal "application/zip", export.file.content_type
+  end
+
+  test "build sets status to processing then completed" do
+    export = Account::Export.create!(account: Current.account, user: users(:david))
+
+    export.build
+
+    assert export.completed?
+    assert_not_nil export.completed_at
+  end
+
+  test "build sends email when completed" do
+    export = Account::Export.create!(account: Current.account, user: users(:david))
+
+    assert_enqueued_jobs 1, only: ActionMailer::MailDeliveryJob do
+      export.build
+    end
+  end
+
+  test "build sets status to failed on error" do
+    export = Account::Export.create!(account: Current.account, user: users(:david))
+    export.stubs(:generate_zip).raises(StandardError.new("Test error"))
+
+    assert_raises(StandardError) do
+      export.build
+    end
+
+    assert export.failed?
+  end
+
+  test "cleanup deletes exports completed more than 24 hours ago" do
+    old_export = Account::Export.create!(account: Current.account, user: users(:david), status: :completed, completed_at: 25.hours.ago)
+    recent_export = Account::Export.create!(account: Current.account, user: users(:david), status: :completed, completed_at: 23.hours.ago)
+    pending_export = Account::Export.create!(account: Current.account, user: users(:david), status: :pending)
+
+    Account::Export.cleanup
+
+    assert_not Account::Export.exists?(old_export.id)
+    assert Account::Export.exists?(recent_export.id)
+    assert Account::Export.exists?(pending_export.id)
+  end
+
+  test "build includes only accessible cards for user" do
+    user = users(:david)
+    export = Account::Export.create!(account: Current.account, user: user)
+
+    export.build
+
+    assert export.completed?
+    assert export.file.attached?
+
+    # Verify zip contents
+    Tempfile.create([ "test", ".zip" ]) do |temp|
+      temp.binmode
+      export.file.download { |chunk| temp.write(chunk) }
+      temp.rewind
+
+      Zip::File.open(temp.path) do |zip|
+        json_files = zip.glob("*.json")
+        assert json_files.any?, "Zip should contain at least one JSON file"
+
+        # Verify structure of a JSON file
+        json_content = JSON.parse(zip.read(json_files.first.name))
+        assert json_content.key?("number")
+        assert json_content.key?("title")
+        assert json_content.key?("board")
+        assert json_content.key?("creator")
+        assert json_content["creator"].key?("id")
+        assert json_content["creator"].key?("name")
+        assert json_content["creator"].key?("email")
+        assert json_content.key?("description")
+        assert json_content.key?("comments")
+      end
+    end
+  end
+end