feat(drive): remove create_home_folder

remove create_home_folder() & ensure_home_folder()

    now: on_user_created() and on_user_login both() call provision_if_needed()
    which calls **create_personal_drive_atomic()**

    add a helper to find Personal drive for a user and also it's root directorry

src/domain/repositories/folder_repository.rs

@@ -136,18 +136,6 @@ pub trait FolderRepository: Send + Sync + 'static {
     /// Permanently deletes a folder (used by the trash)
     async fn delete_folder_permanently(&self, folder_id: &str) -> Result<(), DomainError>;
 
-    /// Creates a root-level home folder for a user inside their personal drive.
-    /// Called during user registration / first login to maintain the wrapper-
-    /// folder convention through the D0 dual-write window (the wrapper itself
-    /// retires in a follow-up migration; for now it stays as a real folder
-    /// row stamped with `drive_id`).
-    async fn create_home_folder(
-        &self,
-        user_id: Uuid,
-        drive_id: Uuid,
-        name: String,
-    ) -> Result<Folder, DomainError>;
-
     /// Lists every folder in a subtree rooted at `folder_id` (inclusive).
     ///
     /// Uses ltree `<@` for a single GiST-indexed scan.  The result is