Redesign the auth background and drop the icon badge.

The login/register backdrop (fluffy white cloud blobs + sun glow) read
as cheap. Replace it with a calmer, more premium take that stays in the
landing's blue/glass language: a deep brand gradient, a faint
infrastructure grid masked toward the edges, soft brand-blue glows and a
vignette. Remove the icon chip above the title on both pages.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/app/[lang]/login/page.tsx

@@ -3,7 +3,7 @@
 import { useState } from 'react';
 import { useAuthStore } from '@/lib/store';
 import { notify } from '@/lib/notify';
-import { LogIn, ArrowLeft } from 'lucide-react';
+import { ArrowLeft } from 'lucide-react';
 import { AuthShell } from '@/components/auth/AuthShell';
 import { AuthField } from '@/components/auth/AuthField';
 import { useT } from '@/i18n/I18nProvider';
@@ -33,7 +33,6 @@ export default function LoginPage() {
 
   return (
     <AuthShell
-      icon={<LogIn className="h-7 w-7" />}
       title={tl.title}
       subtitle={tl.subtitle}
       altPrompt={tl.altPrompt}

frontend/src/app/[lang]/register/page.tsx

@@ -3,7 +3,7 @@
 import { useState } from 'react';
 import { useAuthStore } from '@/lib/store';
 import { notify } from '@/lib/notify';
-import { UserPlus, ArrowLeft } from 'lucide-react';
+import { ArrowLeft } from 'lucide-react';
 import { AuthShell } from '@/components/auth/AuthShell';
 import { AuthField } from '@/components/auth/AuthField';
 import { useT } from '@/i18n/I18nProvider';
@@ -32,7 +32,6 @@ export default function RegisterPage() {
 
   return (
     <AuthShell
-      icon={<UserPlus className="h-7 w-7" />}
       title={tr.title}
       subtitle={tr.subtitle}
       altPrompt={tr.altPrompt}