fix(ocr): reduce async queue capacity from 100 to 10

Queue capacity of 100 is disproportionate for 2 worker threads — a
backed-up queue would represent hours of unprocessed OCR jobs.

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

backend/src/main/java/org/raddatz/familienarchiv/config/AsyncConfig.java

@@ -18,7 +18,7 @@ public class AsyncConfig {
         ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
         executor.setCorePoolSize(2);
         executor.setMaxPoolSize(2);
-        executor.setQueueCapacity(100);
+        executor.setQueueCapacity(10);
         executor.setThreadNamePrefix("Async-");
         executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
         return executor;