feat(store): add blob, file, folder, and upload stores

Add BlobStore (ref counting), FileStore (soft delete + pagination), FolderStore (materialized path), UploadStore (idempotent upsert), and update AutoMigrate.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/store/folder_store.go

@@ -0,0 +1,105 @@
+package store
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"gcy_hpc_server/internal/model"
+
+	"gorm.io/gorm"
+)
+
+type FolderStore struct {
+	db *gorm.DB
+}
+
+func NewFolderStore(db *gorm.DB) *FolderStore {
+	return &FolderStore{db: db}
+}
+
+func (s *FolderStore) Create(ctx context.Context, folder *model.Folder) error {
+	return s.db.WithContext(ctx).Create(folder).Error
+}
+
+func (s *FolderStore) GetByID(ctx context.Context, id int64) (*model.Folder, error) {
+	var folder model.Folder
+	err := s.db.WithContext(ctx).First(&folder, id).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &folder, nil
+}
+
+func (s *FolderStore) GetByPath(ctx context.Context, path string) (*model.Folder, error) {
+	var folder model.Folder
+	err := s.db.WithContext(ctx).Where("path = ?", path).First(&folder).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &folder, nil
+}
+
+func (s *FolderStore) ListByParentID(ctx context.Context, parentID *int64) ([]model.Folder, error) {
+	var folders []model.Folder
+	query := s.db.WithContext(ctx)
+	if parentID == nil {
+		query = query.Where("parent_id IS NULL")
+	} else {
+		query = query.Where("parent_id = ?", *parentID)
+	}
+	if err := query.Order("name ASC").Find(&folders).Error; err != nil {
+		return nil, err
+	}
+	return folders, nil
+}
+
+// GetSubTree returns all folders whose path starts with the given prefix.
+func (s *FolderStore) GetSubTree(ctx context.Context, path string) ([]model.Folder, error) {
+	var folders []model.Folder
+	if err := s.db.WithContext(ctx).Where("path LIKE ?", path+"%").Find(&folders).Error; err != nil {
+		return nil, err
+	}
+	return folders, nil
+}
+
+// HasChildren checks if a folder has sub-folders or files.
+func (s *FolderStore) HasChildren(ctx context.Context, id int64) (bool, error) {
+	folder, err := s.GetByID(ctx, id)
+	if err != nil {
+		return false, err
+	}
+	if folder == nil {
+		return false, nil
+	}
+
+	// Check for sub-folders
+	var subFolderCount int64
+	if err := s.db.WithContext(ctx).Model(&model.Folder{}).Where("parent_id = ?", id).Count(&subFolderCount).Error; err != nil {
+		return false, fmt.Errorf("count sub-folders: %w", err)
+	}
+	if subFolderCount > 0 {
+		return true, nil
+	}
+
+	// Check for files
+	var fileCount int64
+	if err := s.db.WithContext(ctx).Model(&model.File{}).Where("folder_id = ?", id).Count(&fileCount).Error; err != nil {
+		return false, fmt.Errorf("count files: %w", err)
+	}
+	return fileCount > 0, nil
+}
+
+func (s *FolderStore) Delete(ctx context.Context, id int64) error {
+	result := s.db.WithContext(ctx).Delete(&model.Folder{}, id)
+	if result.Error != nil {
+		return result.Error
+	}
+	return nil
+}