Replace the placeholder Step 0 with two clickable mode-card buttons (create new vault / attach this device). Picking a card highlights it and enables the next button; the back button on Step 1 returns to Step 0 without losing state. Add .mode-card CSS using the existing dark palette (#30363d, #58a6ff). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>