feat(korrespondenz): address PR #164 review – blockers and suggestions

Blockers (14):
- B1: fix senderName/receiverName to use $derived instead of $state + sync $effect
- B2: migrate all korrespondenz components from messages-extra shim to paraglide m.*
- B3: i18n CorrespondenzEmptyState (heading, subtext, search placeholder)
- B4: add response.ok checks to admin layout server load
- B5: add response.ok checks to korrespondenz page server load
- B6: add page.server.spec.ts with 5 test suites for korrespondenz load function
- B7: add axe-core accessibility checks to all e2e korrespondenz tests
- B8: add Testcontainers JPQL tests for findSinglePersonCorrespondence (DISTINCT + sender)
- B9: hide auth reset-token endpoint from OpenAPI spec; remove from generated api.ts
- B11: replace amber hardcoded hex colors in SinglePersonHintBar with brand tokens
- B12: replace clipboard emoji with Heroicons SVG in SinglePersonHintBar
- B13: create DateInput component (German dd.mm.yyyy); use it in CorrespondenzFilterControls
- B14: add Paraglide compile step to CI workflow before lint/test

Suggestions (11):
- S1: make CorrespondentSuggestionsDropdown a pure display component; lift fetch to PersonBar
- S2: fix leftover messages-extra import in ConversationTimeline; use brand tokens for status dots
- S3: add intent comment to EntityNav openFlyout behavior
- S4: rename canManageGroups → canManagePermissions throughout admin
- S6: remove domFlush helper from DateInput spec; use expect.poll instead
- S7: replace test.skip with throw new Error in bilateral e2e tests
- S8: add inverse aria-disabled test for filter strip
- S9: remove sm:min-h-0 from sort button to preserve 44px touch target
- S10: add title attributes to tablet trigger buttons in EntityNav
- S11: delete messages-extra.ts shim entirely

Also: fix admin pages revealing blank strip at bottom (-mb-6 on admin layout)

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

backend/src/test/java/org/raddatz/familienarchiv/repository/DocumentRepositoryTest.java

@@ -15,8 +15,11 @@ import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Sort;
 
+import java.time.LocalDate;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
+import java.util.Set;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -189,4 +192,65 @@ class DocumentRepositoryTest {
         assertThat(result.getTotalElements()).isEqualTo(5);
         assertThat(result.getContent()).allMatch(d -> !d.isMetadataComplete());
     }
+
+    // ─── findSinglePersonCorrespondence — DISTINCT / multi-receiver safety ────
+
+    @Test
+    void findSinglePersonCorrespondence_returnsExactlyOneResult_whenDocumentHasThreeReceiversAndOneMatchesPersonId() {
+        Person sender = personRepository.save(Person.builder()
+                .firstName("Hans").lastName("Müller").build());
+        Person receiver1 = personRepository.save(Person.builder()
+                .firstName("Anna").lastName("Schmidt").build());
+        Person receiver2 = personRepository.save(Person.builder()
+                .firstName("Bertha").lastName("Wagner").build());
+        Person receiver3 = personRepository.save(Person.builder()
+                .firstName("Clara").lastName("Koch").build());
+
+        // Document addressed to all three receivers
+        Document doc = documentRepository.save(Document.builder()
+                .title("Rundschreiben")
+                .originalFilename("rundschreiben.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(sender)
+                .receivers(new HashSet<>(Set.of(receiver1, receiver2, receiver3)))
+                .documentDate(LocalDate.of(1950, 6, 1))
+                .build());
+
+        Sort sort = Sort.by(Sort.Direction.DESC, "documentDate");
+        LocalDate from = LocalDate.of(1900, 1, 1);
+        LocalDate to = LocalDate.of(2000, 1, 1);
+
+        // Query for receiver1 — the DISTINCT must collapse the 3 JOIN rows into 1 result
+        List<Document> results = documentRepository.findSinglePersonCorrespondence(
+                receiver1.getId(), from, to, sort);
+
+        assertThat(results).hasSize(1);
+        assertThat(results.get(0).getId()).isEqualTo(doc.getId());
+    }
+
+    @Test
+    void findSinglePersonCorrespondence_includesDocumentsWherePerson_isSender() {
+        Person sender = personRepository.save(Person.builder()
+                .firstName("Hans").lastName("Müller").build());
+        Person receiver = personRepository.save(Person.builder()
+                .firstName("Anna").lastName("Schmidt").build());
+
+        documentRepository.save(Document.builder()
+                .title("Brief als Absender")
+                .originalFilename("brief_absender.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .sender(sender)
+                .receivers(new HashSet<>(Set.of(receiver)))
+                .documentDate(LocalDate.of(1950, 6, 1))
+                .build());
+
+        Sort sort = Sort.by(Sort.Direction.DESC, "documentDate");
+        LocalDate from = LocalDate.of(1900, 1, 1);
+        LocalDate to = LocalDate.of(2000, 1, 1);
+
+        List<Document> results = documentRepository.findSinglePersonCorrespondence(
+                sender.getId(), from, to, sort);
+
+        assertThat(results).hasSize(1);
+    }
 }