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/mysql.go

@@ -40,5 +40,12 @@ func NewGormDB(dsn string, zapLogger *zap.Logger, gormLevel string) (*gorm.DB, e
 
 // AutoMigrate runs GORM auto-migration for all models.
 func AutoMigrate(db *gorm.DB) error {
-	return db.AutoMigrate(&model.Application{})
+	return db.AutoMigrate(
+		&model.Application{},
+		&model.FileBlob{},
+		&model.File{},
+		&model.Folder{},
+		&model.UploadSession{},
+		&model.UploadChunk{},
+	)
 }