Add the split-screen auth shell, switch prompt, and password toggle

web/frontend/app/features/auth/components/AuthSplitLayout.tsx

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+interface AuthSplitLayoutProps {
+    headline: string;
+    blurb: string;
+    children: React.ReactNode;
+}
+
+const AuthSplitLayout = ({ headline, blurb, children }: AuthSplitLayoutProps) => (
+    <div className="grid flex-1 grid-cols-1 bg-base-200 lg:grid-cols-[minmax(0,5fr)_minmax(0,6fr)]">
+        <aside className="flex flex-col justify-end gap-5 bg-secondary px-5 py-7 text-secondary-content lg:px-14 lg:py-12">
+            <h2 className="text-3xl leading-[1.15] text-balance lg:text-[2.75rem]">{headline}</h2>
+            <p className="max-w-[23.75rem] text-base leading-relaxed lg:text-lg">{blurb}</p>
+        </aside>
+
+        <main className="flex items-start justify-center px-5 pt-7 pb-10 lg:items-center lg:px-6 lg:py-10">
+            {children}
+        </main>
+    </div>
+);
+
+export default AuthSplitLayout;

web/frontend/app/features/auth/components/AuthSwitchPrompt.tsx

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+import { Link } from 'react-router';
+
+interface AuthSwitchPromptProps {
+    lead: string;
+    to: string;
+    label: string;
+}
+
+const AuthSwitchPrompt = ({ lead, to, label }: AuthSwitchPromptProps) => (
+    <p className="text-center text-[0.9375rem] text-[var(--color-muted)]">
+        {lead}{' '}
+        <Link to={to} className="font-semibold text-secondary hover:text-primary">
+            {label}
+        </Link>
+    </p>
+);
+
+export default AuthSwitchPrompt;

web/frontend/app/features/auth/components/ShowPasswordToggle.tsx

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+import { Button } from '@headlessui/react';
+
+interface ShowPasswordToggleProps {
+    shown: boolean;
+    onToggle: () => void;
+}
+
+const ShowPasswordToggle = ({ shown, onToggle }: ShowPasswordToggleProps) => (
+    <Button
+        type="button"
+        onClick={onToggle}
+        className="inline-flex min-h-11 items-center self-start text-[0.9375rem] font-semibold text-secondary hover:underline"
+    >
+        {shown ? 'Hide password' : 'Show password'}
+    </Button>
+);
+
+export default ShowPasswordToggle;