const rules = {
required: (v) => v.trim() !== '' || 'This field is required.',
email: (v) => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(v) || 'Enter a valid email.',
min: (n) => (v) => v.length >= n || `Minimum ${n} characters required.`,
max: (n) => (v) => v.length <= n || `Maximum ${n} characters allowed.`,
