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,