Add the shadcn login-01 and signup-03 blocks (with the base-luma field/label
components) and wire their forms to the Better Auth client: login →
signIn.email, signup → signUp.email (12-char rule, confirm match), with error
+ submitting states. Dropped the non-functional "Login with Google" button.
Render the block forms from the existing (auth)/login and (auth)/signup pages
(deleting the blocks' duplicate app/login + app/signup routes). Replace the
animated AuthShell with a static, card-based shell + brand header so
onboarding/verify/reset/accept-invite match. Drop the unsupported `eslint`
key from next.config.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>