fix(#147): replace text-accent with text-primary on all text elements

--c-accent (#a1dcd8 light / #00c7b1 dark) is a decorative mint token —
1.52:1 on white, nowhere near WCAG AA. Every place it appeared as the
colour of a text label or interactive button is switched to text-primary
(#012851, 16.8:1 on white) with hover:text-ink-2 for consistency.

Affected: UsersTab, GroupsTab, CommentThread (Reply), DocumentList
(Clear search), PdfViewer (Direkt öffnen link).

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

frontend/src/lib/components/CommentThread.svelte

@@ -277,7 +277,7 @@ onMount(async () => {
 		{#if showReplyButton && canComment}
 			<div class="mt-1">
 				<button
-					class="font-sans text-xs font-medium text-accent transition-colors hover:text-ink"
+					class="font-sans text-xs font-medium text-primary transition-colors hover:text-ink-2"
 					onclick={() => startReply(threadId)}
 				>
 					{m.comment_btn_reply()}