feat(#113): 100% blob storage model — PostgreSQL metadata + DedupService blobs

BREAKING CHANGE: Storage model completely rewritten. All file/folder
metadata now lives in PostgreSQL (storage schema). File content stored
as content-addressable blobs via DedupService. Filesystem directories
are no longer used for user storage.

New components:
- storage.folders / storage.files / storage.trash_items (PG schema)
- FolderDbRepository: virtual folders backed by PG
- FileBlobReadRepository: file reads via PG metadata + dedup blobs
- FileBlobWriteRepository: file writes via PG metadata + dedup blobs
- TrashDbRepository: soft-delete trash using is_trashed flags

Removed legacy FS components (~5500 lines deleted):
- FolderFsRepository, FileFsReadRepository, FileFsWriteRepository
- CompositeFileRepository, ParallelFileProcessor
- IdMappingService, IdMappingOptimizer, FileMetadataCache
- BufferPool, FileSystemUtils, RepositoryErrors
- TrashFsRepository, FolderFsRepositoryTrash

DI rewired: build_app_state() now requires PgPool (no FS fallback).
FileUploadService.new_with_read() and FileRetrievalService.new_with_cache()
constructors added for blob model (no write-behind needed).

Closes #113

src/lib.rs

@@ -8,11 +8,6 @@ pub mod interfaces;
 // Common public re-exports
 pub use application::services::folder_service::FolderService;
 pub use application::services::i18n_application_service::I18nApplicationService;
-pub use application::services::storage_mediator::{FileSystemStorageMediator, StorageMediator};
 pub use domain::services::path_service::StoragePath;
-pub use infrastructure::repositories::CompositeFileRepository;
-pub use infrastructure::repositories::folder_fs_repository::FolderFsRepository;
-pub use infrastructure::repositories::parallel_file_processor::ParallelFileProcessor;
-pub use infrastructure::services::buffer_pool::BufferPool;
 pub use infrastructure::services::compression_service::GzipCompressionService;
 pub use infrastructure::services::path_service::PathService;