fix(dump): stream files during restore to avoid memory pressure

Use a temporary file instead of io.ReadAll when restoring attachments
from a dump. This prevents loading entire files into memory, which could
cause OOM errors for large attachments during restore.

pkg/modules/dump/restore.go

@@ -174,21 +174,8 @@ func Restore(filename string, overrideConfig bool) error {
 			return fmt.Errorf("could not parse file id %s: %w", i, err)
 		}
 
-		f := &files.File{ID: id}
-
-		fc, err := file.Open()
-		if err != nil {
-			return fmt.Errorf("could not open file %s: %w", i, err)
-		}
-
-		content, err := io.ReadAll(fc)
-		_ = fc.Close()
-		if err != nil {
-			return fmt.Errorf("could not read file %s: %w", i, err)
-		}
-
-		if err := f.Save(bytes.NewReader(content)); err != nil {
-			return fmt.Errorf("could not save file: %w", err)
+		if err := restoreFile(id, file); err != nil {
+			return fmt.Errorf("could not restore file %s: %w", i, err)
 		}
 		log.Infof("Restored file %s", i)
 	}
@@ -204,6 +191,38 @@ func Restore(filename string, overrideConfig bool) error {
 	return nil
 }
 
+func restoreFile(id int64, zipFile *zip.File) error {
+	f := &files.File{ID: id}
+
+	fc, err := zipFile.Open()
+	if err != nil {
+		return fmt.Errorf("could not open zip entry: %w", err)
+	}
+	defer fc.Close()
+
+	// Create a temporary file to make the content seekable without loading
+	// it all into memory. zip.File.Open() returns io.ReadCloser which is not
+	// seekable, but f.Save requires io.ReadSeeker.
+	tmpFile, err := os.CreateTemp("", "vikunja-restore-*")
+	if err != nil {
+		return fmt.Errorf("could not create temp file: %w", err)
+	}
+	defer func() {
+		_ = tmpFile.Close()
+		_ = os.Remove(tmpFile.Name())
+	}()
+
+	if _, err := io.Copy(tmpFile, fc); err != nil {
+		return fmt.Errorf("could not copy to temp file: %w", err)
+	}
+
+	if _, err := tmpFile.Seek(0, io.SeekStart); err != nil {
+		return fmt.Errorf("could not seek temp file: %w", err)
+	}
+
+	return f.Save(tmpFile)
+}
+
 func convertFieldValue(fieldName string, value interface{}, isFloat bool) (interface{}, error) {
 	// Check if this is a float field and the value is already a number
 	if isFloat {