fix(login): add role=alert to error divs; fix clock icon color to red

Regular error div was missing role="alert" — screen readers did not
announce it on dynamic display. Rate-limited clock icon used text-ink-3
(muted grey) instead of text-red-600, visually inconsistent with the
surrounding error text. Also removes the erroneous aria-invalid="true"
from the rate-limit alert div (not a permitted attribute on role=alert).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/login/+page.svelte

@@ -108,7 +108,6 @@ let {
 					{#if form?.error}
 						{#if form?.rateLimited}
 							<div
-								aria-invalid="true"
 								role="alert"
 								class="flex items-center gap-2 font-sans text-xs font-medium text-red-600"
 							>
@@ -118,7 +117,7 @@ let {
 									fill="none"
 									stroke="currentColor"
 									stroke-width="1.5"
-									class="h-4 w-4 shrink-0 text-ink-3"
+									class="h-4 w-4 shrink-0 text-red-600"
 								>
 									<path
 										stroke-linecap="round"
@@ -129,7 +128,9 @@ let {
 								<span>{form.error}</span>
 							</div>
 						{:else}
-							<div class="text-center font-sans text-xs font-medium text-red-600">{form.error}</div>
+							<div role="alert" class="text-center font-sans text-xs font-medium text-red-600">
+								{form.error}
+							</div>
 						{/if}
 					{/if}