complete onboarding UX v2

Tasks C, H, I from the plan:

- Forgiving API key validation: add Printify UUID format and Printful
  length validation, validate on blur for fast feedback, helpful error
  messages with specific guidance

- External links UX: verified all external links use <.external_link>
  component with target="_blank", rel="noopener noreferrer", icon, and
  screen reader text

- Input styling WCAG compliance: increase input border contrast from
  ~3.3:1 to ~4.5-5:1 across all theme moods (neutral, warm, cool, dark)

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

test/berrypod_web/live/admin/dashboard_test.exs

@@ -28,9 +28,9 @@ defmodule BerrypodWeb.Admin.DashboardTest do
 
       assert html =~ "Launch checklist"
       assert html =~ "Connect a print provider"
-      assert html =~ "Connect Stripe"
-      assert html =~ "Sync your products"
-      assert html =~ "Customise your theme"
+      assert html =~ "Connect Stripe for payments"
+      assert html =~ "Import products"
+      assert html =~ "Customise your shop"
       assert html =~ "Go live"
     end
 
@@ -43,16 +43,16 @@ defmodule BerrypodWeb.Admin.DashboardTest do
 
     test "collapse and expand checklist", %{conn: conn} do
       {:ok, view, html} = live(conn, ~p"/admin")
-      assert html =~ "Sync your products"
+      assert html =~ "Import products"
 
       # Collapse
       html = render_click(view, "toggle_checklist")
-      refute html =~ "Sync your products"
+      refute html =~ "Import products"
       assert html =~ "Launch checklist"
 
       # Expand
       html = render_click(view, "toggle_checklist")
-      assert html =~ "Sync your products"
+      assert html =~ "Import products"
     end
 
     test "go live button works", %{conn: conn} do