feat: add file deduplication and hash checking for uploads

- Implemented SHA-256 hashing for uploaded files to enable deduplication.
- Added CheckHash method to verify if a file with the same hash already exists.
- Updated Upload method to reuse existing media assets if a duplicate is found.
- Introduced a new hash column in the media_assets table to store file hashes.
- Enhanced the upload process to include progress tracking and hash calculation.
- Modified frontend to check for existing files before uploading and to show upload progress.
- Added vuedraggable for drag-and-drop functionality in the content editing view.

backend/database/models/media_assets.gen.go

@@ -34,6 +34,7 @@ type MediaAsset struct {
 	CreatedAt     time.Time                             `gorm:"column:created_at;type:timestamp with time zone;default:now()" json:"created_at"`
 	UpdatedAt     time.Time                             `gorm:"column:updated_at;type:timestamp with time zone;default:now()" json:"updated_at"`
 	DeletedAt     gorm.DeletedAt                        `gorm:"column:deleted_at;type:timestamp with time zone" json:"deleted_at"`
+	Hash          string                                `gorm:"column:hash;type:character varying(64);comment:File SHA-256 hash" json:"hash"` // File SHA-256 hash
 }
 
 // Quick operations without importing query package