feat(files): add v2 task and metadata workflows

backend/src/main/java/com/yoyuzh/files/NoopBackgroundTaskHandler.java

@@ -0,0 +1,30 @@
+package com.yoyuzh.files;
+
+import org.springframework.stereotype.Component;
+
+import java.time.LocalDateTime;
+import java.util.Map;
+import java.util.Set;
+
+@Component
+public class NoopBackgroundTaskHandler implements BackgroundTaskHandler {
+
+    private static final Set<BackgroundTaskType> SUPPORTED_TYPES = Set.of(
+            BackgroundTaskType.ARCHIVE,
+            BackgroundTaskType.EXTRACT
+    );
+
+    @Override
+    public boolean supports(BackgroundTaskType type) {
+        return SUPPORTED_TYPES.contains(type);
+    }
+
+    @Override
+    public BackgroundTaskHandlerResult handle(BackgroundTask task) {
+        return new BackgroundTaskHandlerResult(Map.of(
+                "worker", "noop",
+                "message", "worker skeleton accepted task without running real file processing",
+                "completedAt", LocalDateTime.now().toString()
+        ));
+    }
+}