fix(ocr): handle unknown NDJSON fields with @JsonIgnoreProperties

Added @JsonIgnoreProperties(ignoreUnknown = true) to OcrBlockResult so
new fields from the Python OCR service don't crash the Java parser,
while keeping FAIL_ON_UNKNOWN_PROPERTIES strict globally.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/service/OcrBlockResult.java

@@ -1,7 +1,10 @@
 package org.raddatz.familienarchiv.service;
 
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+
 import java.util.List;
 
+@JsonIgnoreProperties(ignoreUnknown = true)
 public record OcrBlockResult(
         int pageNumber,
         double x,

backend/src/test/java/org/raddatz/familienarchiv/service/RestClientOcrClientStreamTest.java

@@ -98,6 +98,23 @@ class RestClientOcrClientStreamTest {
         assertThat(events).hasSize(2);
     }
 
+    @Test
+    void parseNdjsonStream_handlesUnknownFieldsInBlocks() {
+        String ndjson = """
+                {"type":"start","totalPages":1}
+                {"type":"page","pageNumber":0,"blocks":[{"pageNumber":0,"x":0.1,"y":0.2,"width":0.8,"height":0.1,"polygon":null,"text":"Line 1","confidence":0.95,"newFutureField":"ignored"}]}
+                {"type":"done","totalBlocks":1,"skippedPages":0}
+                """;
+        InputStream stream = new ByteArrayInputStream(ndjson.getBytes(StandardCharsets.UTF_8));
+
+        List<OcrStreamEvent> events = new ArrayList<>();
+        RestClientOcrClient.parseNdjsonStream(stream, events::add);
+
+        assertThat(events).hasSize(3);
+        var page = (OcrStreamEvent.Page) events.get(1);
+        assertThat(page.blocks().get(0).text()).isEqualTo("Line 1");
+    }
+
     @Test
     void parseNdjsonStream_parsesPageWithPolygon() {
         String ndjson = """