fix(dashboard): i18n, a11y, security, and type-safety fixes from PR review

- Use @RequiredArgsConstructor in AuditLogQueryService; remove unused import
- Add 401/403 tests for /activity endpoint
- Add getPulseStats and findContributorsPerDocument integration tests
- Use m.pulse_headline/pulse_you in FamilyPulse; composite avatar keys
- Replace hover:text-accent with hover:text-ink in ActivityFeed (WCAG AA)
- Localise "Alle →" link with feed_show_all key + aria-label
- Gate DropZone behind {#if data.canWrite}
- Export DashboardResumeDTO, DashboardPulseDTO, ActivityFeedItemDTO from api.ts

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

frontend/src/routes/+page.svelte

@@ -151,7 +151,9 @@ const greetingText = $derived.by(() => {
 			<div class="flex flex-col gap-5 lg:sticky lg:top-[80px]">
 				<DashboardFamilyPulse pulse={data.pulse ?? null} />
 				<DashboardActivityFeed feed={data.activityFeed ?? []} />
-				<DropZone />
+				{#if data.canWrite}
+					<DropZone />
+				{/if}
 			</div>
 		</div>
 	{:else}