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/routes/admin/GroupsTab.svelte

@@ -135,7 +135,7 @@ function cancelEditGroup() {
 							<div class="flex items-center justify-end gap-3">
 								<button
 									onclick={() => startEditGroup(group.id)}
-									class="text-sm font-bold tracking-wide text-accent uppercase hover:text-ink"
+									class="text-sm font-bold tracking-wide text-primary uppercase hover:text-ink-2"
 								>
 									{m.btn_edit()}
 								</button>

frontend/src/routes/admin/UsersTab.svelte

@@ -78,7 +78,7 @@ let {
 						<div class="flex items-center justify-end gap-4">
 							<a
 								href="/admin/users/{user.id}"
-								class="text-sm font-bold tracking-wide text-accent uppercase hover:text-ink"
+								class="text-sm font-bold tracking-wide text-primary uppercase hover:text-ink-2"
 							>
 								{m.btn_edit()}
 							</a>