refactor: reorganize project structure and update configurations

- Move migrations/ to database/schema/ for clarity on database schema definitions
- Move sqlc.yaml to internal/database/ to group with database code
- Move static/ to cmd/server/static/ to co-locate with server
- Update all configuration files and documentation
- Follow Go project conventions for better organization

internal/database/queries.sql.go

@@ -223,8 +223,8 @@ func (q *Queries) DeleteUser(ctx context.Context, id pgtype.UUID) error {
 	return err
 }
 
-const DeleteUserEbookFolder = `-- name: DeleteUserEbookFolder :exec
-DELETE FROM user_ebook_folders WHERE user_id = $1 AND folder_path = $2
+const DeleteUserEbookFolder = `-- name: DeleteUserEbookFolder :one
+DELETE FROM user_ebook_folders WHERE user_id = $1 AND folder_path = $2 RETURNING id, user_id, folder_path, created_at
 `
 
 type DeleteUserEbookFolderParams struct {
@@ -232,9 +232,16 @@ type DeleteUserEbookFolderParams struct {
 	FolderPath string      `db:"folder_path" json:"folder_path"`
 }
 
-func (q *Queries) DeleteUserEbookFolder(ctx context.Context, arg DeleteUserEbookFolderParams) error {
-	_, err := q.db.Exec(ctx, DeleteUserEbookFolder, arg.UserID, arg.FolderPath)
-	return err
+func (q *Queries) DeleteUserEbookFolder(ctx context.Context, arg DeleteUserEbookFolderParams) (UserEbookFolders, error) {
+	row := q.db.QueryRow(ctx, DeleteUserEbookFolder, arg.UserID, arg.FolderPath)
+	var i UserEbookFolders
+	err := row.Scan(
+		&i.ID,
+		&i.UserID,
+		&i.FolderPath,
+		&i.CreatedAt,
+	)
+	return i, err
 }
 
 const GetEbook = `-- name: GetEbook :one