fix(#145): address PR review — full-table scan, a11y, grid, tests

- DocumentService.getRecentActivity: replace findAll(Sort)+stream().limit()
  with findAll(PageRequest) so LIMIT is pushed to the database
- +page.svelte: collapse two-column grid to single column when mentions is empty
- DashboardNeedsMetadata: raise "show all" link from text-xs (12px) to text-sm
  (14px) and add hover:underline for WCAG 1.4.1
- DashboardRecentDocuments: add comment explaining why T12:00:00 noon-anchor
  is absent (updatedAt is a full ISO datetime, not a date-only string)
- DocumentServiceTest: update getRecentActivity tests to assert PageRequest
  usage instead of findAll(Sort)
- DocumentRepositoryTest: add @DataJpaTest verifying findAll(PageRequest)
  returns only size rows, not the full table
- DocumentControllerTest: add test for default size=5 when param is omitted
- NotificationServiceTest: add test documenting that type+read=true falls
  through to the type-only query (intentional)
- page.server.spec.ts: replace stale tests with full dashboard-mode coverage
- DashboardMentions.svelte.spec.ts: add tests for REPLY type and absent documentId
- DashboardResumeStrip.svelte.spec.ts: add corrupt localStorage test

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

frontend/src/lib/components/DashboardNeedsMetadata.svelte

@@ -29,7 +29,7 @@ let { incompleteDocs }: Props = $props();
 			</div>
 		{/each}
 		<div class="mt-4">
-			<a href="/enrich" class="font-sans text-xs text-ink-2 hover:text-ink"
+			<a href="/enrich" class="font-sans text-sm text-ink-2 hover:text-ink hover:underline"
 				>{m.dashboard_needs_metadata_show_all()}</a
 			>
 		</div>