docs: update documentation to reflect 100% blob storage model

Rewrite documentation to match the new architecture where all
file metadata lives in PostgreSQL and content is stored as
content-addressed blobs via DedupService.

Updated files:
- internal-architecture.md: complete rewrite — new DB schema,
  blob repos (FolderDb, FileBlobRead/Write, TrashDb), updated
  DI container, service groups, architecture diagram, data flows
- file-system-safety.md: repurposed as storage-safety.md —
  covers PostgreSQL ACID guarantees + DedupService atomic writes
- caching-architecture.md: updated repo references to blob repos,
  removed write-behind cache section, updated upload/download flows
- trash-feature-summary.md: rewritten for soft-delete model
  (is_trashed flag, trash_items VIEW, TrashDbRepository)
- share-integration.md: clarified ShareFsRepository scope,
  updated DI snippet, added blob storage context note
- deduplication.md: updated DI snippet (dedup injected into repos)
- deployment.md: updated feature matrix (file storage requires DB)
- important-delta-sync-implementation.md: updated DI references

Removed legacy references: IdMappingPort, StorageMediator,
WriteBehindCache, FsFileRepository, FsFolderRepository,
TrashFsRepository, folder_ids.json, file_ids.json.

doc/deduplication.md

@@ -285,9 +285,12 @@ pub struct CoreServices {
     // ...
 }
 
-// Injected into application services:
-FileUploadService::new_full(... core.dedup_service.clone())
-FileManagementService::new_full(... core.dedup_service.clone())
+// Injected into blob repositories (which handle dedup internally):
+FileBlobReadRepository::new(pool, core.dedup_service.clone(), folder_repo)
+FileBlobWriteRepository::new(pool, core.dedup_service.clone(), folder_repo)
+
+// Also injected into FileManagementService for ref cleanup on delete:
+FileManagementService::new_full(write, read, trash, core.dedup_service.clone())
 ```
 
 ## Persistence