refactor(theming): replace red-* palette with semantic error-* tokens

Sweep 30 files: text/bg/border/ring/from/to/via/fill/stroke/shadow/divide/decoration/
outline/placeholder-red-N → -error-N. All red usages were semantically error/danger
(no brand red), so tokens now flow through the design-system CSS variables and respond
to palette overrides.

src/pages/VerifyEmail.tsx

@@ -102,7 +102,7 @@ export default function VerifyEmail() {
 
         {status === 'error' && (
           <div>
-            <div className="mb-4 text-5xl text-red-500 sm:text-6xl">✗</div>
+            <div className="mb-4 text-5xl text-error-500 sm:text-6xl">✗</div>
             <h2 className="text-lg font-semibold text-gray-900 sm:text-xl">
               {t('emailVerification.failed')}
             </h2>