feat: folder ownership scoping, batch operations integration, frontend audit fixes

Backend:
- Add owner_id to Folder entity + FolderDto (DB user_id column)
- Add list_folders_by_owner to FolderRepository trait + PG impl
- Add list_folders_for_owner to FolderUseCase + FolderService
- Rewrite FolderHandler: all endpoints now scope by AuthUser
- Remove dead handler methods (list_folders_inner, list_folders_for_user, is_user_home_folder, folder_belongs_to_user)
- Add ownership check in get_folder (returns 404 on mismatch)

Batch operations:
- Add trash_service + zip_service to BatchOperationService
- New methods: trash_files, trash_folders, move_folders, download_zip
- New handlers: trash_batch, move_folders_batch, download_batch
- New routes: POST /api/batch/trash, /api/batch/folders/move, /api/batch/download

Frontend:
- Replace findUserHomeFolder (~130 lines) with resolveHomeFolder (~35 lines)
- Remove client-side folder filtering in loadFiles (backend now scopes)
- Rewrite batchDelete: N requests -> 1 POST /api/batch/trash
- Rewrite batchMove: N requests -> 2 POST max (files + folders)
- Rewrite batchDownload: N requests -> 1 POST /api/batch/download (ZIP)
- Search moved to backend, share system uses backend API
- Dark mode fixes, frontend audit improvements

src/application/services/share_service.rs

@@ -154,6 +154,7 @@ impl ShareUseCase for ShareService {
         // Create the Share entity
         let share = Share::new(
             dto.item_id.clone(),
+            dto.item_name.clone(),
             item_type,
             user_id.to_string(),
             permissions,
@@ -524,6 +525,14 @@ mod tests {
             unimplemented!()
         }
 
+        async fn list_folders_by_owner(
+            &self,
+            _parent_id: Option<&str>,
+            _owner_id: &str,
+        ) -> Result<Vec<crate::domain::entities::folder::Folder>, DomainError> {
+            unimplemented!()
+        }
+
         async fn list_folders_paginated(
             &self,
             _parent_id: Option<&str>,