Shell home for the platform-retrofit floor: a sign-in form (dev-seed
credentials) and a signed-in placeholder with sign-out. Both flows run
through the composed tRPC appRouter via server actions that own the
session cookie on the app side; the auth feature is untouched. Adds the
auth sign-in Playwright spec as the surviving e2e baseline and drops the
last demo-template metadata.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK