refactor(backend): switch to DDD

backend/internal/domain/repositories.go

@@ -0,0 +1,16 @@
+package domain
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+)
+
+type FileRepository interface {
+	GetAccess(ctx context.Context, user_id int, file_id string) (canView, canEdit bool, domainErr *DomainError)
+	GetSlice(ctx context.Context, user_id int, filter, sort string, limit, offset int) (files Slice[FileItem], domainErr *DomainError)
+	Get(ctx context.Context, user_id int, file_id string) (file FileFull, domainErr *DomainError)
+	Add(ctx context.Context, user_id int, name, mime string, datetime time.Time, notes string, metadata json.RawMessage) (file FileCore, domainErr *DomainError)
+	Update(ctx context.Context, user_id int, file_id string, updates map[string]interface{}) (domainErr *DomainError)
+	Delete(ctx context.Context, user_id int, file_id string) (domainErr *DomainError)
+}