feat(importing): add precision-aware DocumentTitleFormatter

Adds the Java half of the honest date label — formatTitleDate(date,
precision, end, raw) — mirroring the frontend formatDocumentDate rules so an
import title never shows a precision the data lacks (MONTH → "Juni 1916", not
a fabricated day). Both implementations are pinned to the shared
docs/date-label-fixtures.json table, which this test asserts case-by-case, so
they cannot drift. Java's de CLDR renders the same "Jan."/"Dez." abbreviations
and en-dash the TS side produces.

Refs #666

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/importing/DocumentTitleFormatterTest.java

@@ -0,0 +1,49 @@
+package org.raddatz.familienarchiv.importing;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.DynamicTest;
+import org.junit.jupiter.api.TestFactory;
+import org.raddatz.familienarchiv.document.DatePrecision;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Asserts the Java title label against the SAME shared fixture table the TS
+ * formatter spec uses ({@code docs/date-label-fixtures.json}). This is the
+ * drift guard requested in #666 review: the two label implementations cannot
+ * silently diverge (en-dash vs hyphen, "ca." vs "circa", season words, range
+ * collapse) because both are pinned to one committed rule set.
+ */
+class DocumentTitleFormatterTest {
+
+    @TestFactory
+    List<DynamicTest> matchesSharedFixtureTable() throws Exception {
+        // Maven runs tests from the backend/ module dir; the fixture lives at repo-root docs/.
+        Path fixture = Path.of("..", "docs", "date-label-fixtures.json");
+        JsonNode root = new ObjectMapper().readTree(Files.readString(fixture));
+        List<DynamicTest> tests = new ArrayList<>();
+        for (JsonNode c : root.get("cases")) {
+            String name = c.get("name").asText();
+            LocalDate anchor = parseDate(c.get("anchor"));
+            DatePrecision precision = DatePrecision.valueOf(c.get("precision").asText());
+            LocalDate end = parseDate(c.get("end"));
+            String raw = c.get("raw").isNull() ? null : c.get("raw").asText();
+            String expected = c.get("expected").asText();
+            tests.add(DynamicTest.dynamicTest(name, () ->
+                    assertThat(DocumentTitleFormatter.formatTitleDate(anchor, precision, end, raw))
+                            .isEqualTo(expected)));
+        }
+        return tests;
+    }
+
+    private static LocalDate parseDate(JsonNode node) {
+        return node == null || node.isNull() ? null : LocalDate.parse(node.asText());
+    }
+}