test(document): prove Postgres accepts an equal-date RANGE (#678)

Testcontainers integration test persisting a RANGE doc with end == start
against real Postgres + Flyway, which (unlike H2) enforces the V69
chk_meta_date_end_after_start CHECK. Pins the app guard's isBefore
semantics to the actual >= constraint, guarding against app/DB drift (AC2).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -612,6 +612,29 @@ class DocumentRepositoryTest {
                 .isLessThanOrEqualTo(5);
     }
 
+    // ─── V69 date-range CHECK constraints (#678) ──────────────────────────────
+
+    @Test
+    void save_acceptsRange_whenEndEqualsStart() {
+        // chk_meta_date_end_after_start is end >= start, so equal dates are valid.
+        // Real Postgres + Flyway here (H2 would not enforce the CHECK) pins the
+        // app guard's isBefore semantics to the actual constraint — guards drift (AC2).
+        LocalDate day = LocalDate.of(1917, 1, 10);
+        Document saved = documentRepository.saveAndFlush(Document.builder()
+                .title("Gleicher Tag")
+                .originalFilename("gleicher_tag.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .documentDate(day)
+                .metaDatePrecision(DatePrecision.RANGE)
+                .metaDateEnd(day)
+                .build());
+
+        Document found = documentRepository.findById(saved.getId()).orElseThrow();
+        assertThat(found.getDocumentDate()).isEqualTo(day);
+        assertThat(found.getMetaDateEnd()).isEqualTo(day);
+        assertThat(found.getMetaDatePrecision()).isEqualTo(DatePrecision.RANGE);
+    }
+
     // ─── seeding helpers ─────────────────────────────────────────────────────
 
     private Document uploaded(String title) {