feat(ds): DS::EmptyState primitive (#2137) (#2146)

Ships DS::EmptyState — a centered icon / title / optional description /
optional action-slot state — plus a preview, tests, and an exemplar migration
of the recurring-transactions empty screen.

Consolidates the repeated `text-center py-12 + icon + title + description + CTA`
markup across the empty / no-data screens (recurring, imports, statements,
exports, and several connector setups). The audit flagged the self-hosted
feature-disabled pages rendering bare unstyled top-left text ("reads as a 500,
not a state") — wiring those through this primitive is the follow-up.

- app/components/DS/empty_state.rb: render DS::EmptyState.new(icon:, title:,
  description:) with an optional `with_action` slot for the CTA.
- Migrate recurring_transactions/index empty branch.

Tests + rubocop + erb_lint clean.

Deferred: the remaining ~10 empty screens + the bare-text feature-disabled
states — same primitive, one migration each.

test/components/previews/empty_state_component_preview.rb

@@ -0,0 +1,23 @@
+class EmptyStateComponentPreview < ViewComponent::Preview
+  # @display container_classes max-w-[480px]
+  def default
+    render DS::EmptyState.new(
+      icon: "inbox",
+      title: "No transactions yet",
+      description: "Imported and synced transactions will show up here."
+    )
+  end
+
+  # @display container_classes max-w-[480px]
+  def with_action
+    render DS::EmptyState.new(
+      icon: "repeat",
+      title: "No recurring transactions",
+      description: "We detect patterns automatically, or you can scan now."
+    ) do |es|
+      es.with_action do
+        render DS::Link.new(text: "Scan now", icon: "search", variant: "primary", href: "#")
+      end
+    end
+  end
+end