refactor(layout): consolidate backend codebase into backend/ package and clean root directory

- Moved cmd/, core/, plugins/, pkg/, downstream/, and main.go into backend/ directory
- Batch updated all Go source files to import github.com/Rain-kl/Wavelet/backend/...
- Updated Makefile, scripts/swagger.sh, architecture guards, and platform skills
- Passed all quality gates (100% tests, 0 lint issues, clean build)

backend/plugins/domain/upload/ingest/remove.go

@@ -0,0 +1,58 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package ingest
+
+import (
+	"context"
+
+	uploadcache "github.com/Rain-kl/Wavelet/backend/plugins/domain/upload/cache"
+	"github.com/Rain-kl/Wavelet/backend/plugins/domain/upload/models"
+	"github.com/Rain-kl/Wavelet/backend/plugins/domain/upload/repository"
+	uploadstats "github.com/Rain-kl/Wavelet/backend/plugins/domain/upload/stats"
+	database "github.com/Rain-kl/Wavelet/backend/plugins/infra/database"
+	"gorm.io/gorm"
+)
+
+// Remove soft-deletes an upload and decrements incremental stats.
+func Remove(ctx context.Context, uploadID uint64) (models.Upload, error) {
+	upload, err := repository.GetActiveUploadByID(ctx, uploadID)
+	if err != nil {
+		return models.Upload{}, err
+	}
+	if err := softDeleteUploadWithStats(ctx, &upload); err != nil {
+		return models.Upload{}, err
+	}
+	upload.Status = models.UploadStatusDeleted
+	return upload, nil
+}
+
+// RemoveOwned soft-deletes an upload owned by userID and decrements incremental stats.
+func RemoveOwned(ctx context.Context, userID, uploadID uint64) (models.Upload, error) {
+	upload, err := repository.GetActiveUploadByID(ctx, uploadID)
+	if err != nil {
+		return models.Upload{}, err
+	}
+	if upload.UserID != userID {
+		return models.Upload{}, ErrForbidden
+	}
+	if err := softDeleteUploadWithStats(ctx, &upload); err != nil {
+		return models.Upload{}, err
+	}
+	upload.Status = models.UploadStatusDeleted
+	return upload, nil
+}
+
+func softDeleteUploadWithStats(ctx context.Context, upload *models.Upload) error {
+	statsSnapshot := *upload
+	if err := database.DB(ctx).Transaction(func(tx *gorm.DB) error {
+		if err := repository.SoftDeleteUploadTx(tx, upload); err != nil {
+			return err
+		}
+		return uploadstats.ApplyUploadStatsDeltaTx(tx, &statsSnapshot, -1)
+	}); err != nil {
+		return err
+	}
+	uploadcache.InvalidateUploadMetaCache(ctx, upload.ID)
+	return nil
+}