Use shadcn login-01 / signup-03 card blocks (no animation)

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>

frontend/next.config.ts

@@ -3,12 +3,11 @@ import type { NextConfig } from "next";
 const nextConfig: NextConfig = {
   // Emit a self-contained server build for a small Docker image.
   output: "standalone",
-  // The vendored components/ai-elements/* library has pre-existing type/lint
-  // drift against this Base UI version (see CLAUDE.md), which would otherwise
-  // fail `next build`. Skip those gates so production/Docker builds succeed;
-  // app code is still type-checked separately via `tsc --noEmit`.
+  // The vendored components/ai-elements/* library has pre-existing type drift
+  // against this Base UI version (see CLAUDE.md), which would otherwise fail
+  // `next build`. Skip the type gate so production/Docker builds succeed; app
+  // code is still type-checked separately via `tsc --noEmit`.
   typescript: { ignoreBuildErrors: true },
-  eslint: { ignoreDuringBuilds: true },
 };
 
 export default nextConfig;