feat(uat-batch-21): a11y — auth-page link contrast bumped past AA

`text-[#007bff] hover:underline` (light blue, 12-14px) was falling
below WCAG 1.4.3 AA contrast against the auth shell's white card.
Bumped to `text-[#0058b3]` (darker variant of the same hue) and
added `underline underline-offset-2 hover:no-underline` so the link
is always visibly underlined as a backup affordance.

Affects: /login, /reset-password, /set-password, /portal/login,
/portal/forgot-password, portal password-set-form. Button bg colors
(white-text on the same blue) are unchanged — those pass AA at
button sizes.

tsc clean. 1419/1419 vitest pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/portal/password-set-form.tsx

@@ -128,7 +128,7 @@ export function PasswordSetForm({
           </p>
           <Link
             href="/portal/forgot-password"
-            className="inline-block text-sm text-[#007bff] hover:underline"
+            className="inline-block text-sm text-[#0058b3] underline-offset-2 underline hover:no-underline"
           >
             Request a new link
           </Link>
@@ -148,7 +148,7 @@ export function PasswordSetForm({
           <p className="text-gray-500 text-sm">{successDescription}</p>
           <Link
             href="/portal/login"
-            className="mt-6 inline-block text-sm text-[#007bff] hover:underline"
+            className="mt-6 inline-block text-sm text-[#0058b3] underline-offset-2 underline hover:no-underline"
           >
             Sign in
           </Link>