fix(ocr): increase presigned URL TTL from 15 min to 1 hour

A 100-page document at ~10 s/page takes ~17 min on CPU-only hardware,
which could cause the presigned URL to expire mid-OCR job. 1 hour gives
ample headroom for any realistic document size in this archive.

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

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

@@ -114,7 +114,8 @@ public class FileService {
 
     /**
      * Generates a presigned URL for downloading an object from S3/MinIO.
-     * Valid for 15 minutes — enough for OCR processing on CPU.
+     * Valid for 1 hour — covers multi-page documents on CPU-only OCR hardware
+     * (a 100-page document at 10 s/page takes ~17 min; 1 h gives ample headroom).
      */
     public String generatePresignedUrl(String s3Key) {
         GetObjectRequest getObjectRequest = GetObjectRequest.builder()
@@ -123,7 +124,7 @@ public class FileService {
                 .build();
 
         GetObjectPresignRequest presignRequest = GetObjectPresignRequest.builder()
-                .signatureDuration(Duration.ofMinutes(15))
+                .signatureDuration(Duration.ofHours(1))
                 .getObjectRequest(getObjectRequest)
                 .build();