feat(01-04): add Google button to login and register pages

- Add auth layout with centered card design
- Add Input component for form fields
- Add LoginForm component with email/password and validation
- Add RegisterForm component with password requirements
- Add login page with Google button + 'oppure' divider + email form
- Add register page with Google button + 'oppure' divider + email form
- Italian text throughout (Accedi, Registrati, oppure)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/auth/login-form.tsx

@@ -0,0 +1,103 @@
+'use client'
+
+import { Button } from '@/components/ui/button'
+import { Input } from '@/components/ui/input'
+import Link from 'next/link'
+import { useState } from 'react'
+import { createClient } from '@/lib/supabase/client'
+import { useRouter } from 'next/navigation'
+
+export function LoginForm() {
+  const [email, setEmail] = useState('')
+  const [password, setPassword] = useState('')
+  const [error, setError] = useState<string | null>(null)
+  const [loading, setLoading] = useState(false)
+  const router = useRouter()
+  const supabase = createClient()
+
+  async function handleSubmit(e: React.FormEvent) {
+    e.preventDefault()
+    setError(null)
+    setLoading(true)
+
+    const { error: signInError } = await supabase.auth.signInWithPassword({
+      email,
+      password,
+    })
+
+    if (signInError) {
+      // SPECIFIC error messages per user requirement
+      if (signInError.message.includes('Invalid login credentials')) {
+        setError('Email o password errata')
+      } else if (signInError.message.includes('Email not confirmed')) {
+        setError('Devi confermare la tua email prima di accedere')
+      } else {
+        setError(signInError.message)
+      }
+      setLoading(false)
+      return
+    }
+
+    router.push('/dashboard')
+    router.refresh()
+  }
+
+  return (
+    <form onSubmit={handleSubmit} className="space-y-4">
+      {error && (
+        <div className="p-3 bg-red-50 border border-red-200 rounded-md">
+          <p className="text-red-800 text-sm">{error}</p>
+        </div>
+      )}
+
+      <div>
+        <label htmlFor="email" className="block text-sm font-medium text-gray-700 mb-1">
+          Email
+        </label>
+        <Input
+          id="email"
+          name="email"
+          type="email"
+          autoComplete="email"
+          required
+          placeholder="tu@esempio.com"
+          value={email}
+          onChange={(e) => setEmail(e.target.value)}
+        />
+      </div>
+
+      <div>
+        <label htmlFor="password" className="block text-sm font-medium text-gray-700 mb-1">
+          Password
+        </label>
+        <Input
+          id="password"
+          name="password"
+          type="password"
+          autoComplete="current-password"
+          required
+          placeholder="La tua password"
+          value={password}
+          onChange={(e) => setPassword(e.target.value)}
+        />
+      </div>
+
+      <div className="flex items-center justify-end">
+        <Link href="/reset-password" className="text-sm text-blue-600 hover:underline">
+          Password dimenticata?
+        </Link>
+      </div>
+
+      <Button type="submit" className="w-full" disabled={loading}>
+        {loading ? 'Accesso...' : 'Accedi'}
+      </Button>
+
+      <p className="text-center text-sm text-gray-600">
+        Non hai un account?{' '}
+        <Link href="/register" className="text-blue-600 hover:underline">
+          Registrati
+        </Link>
+      </p>
+    </form>
+  )
+}