perf: findings 6.1, 6.2, 2.6 — async Argon2, moka cache, full streaming migration

- 6.1: PasswordHasherPort now async_trait with spawn_blocking for Argon2
- 6.2: OIDC pending maps migrated from std::sync::Mutex to moka::sync::Cache with TTL
- 2.6: All file download paths migrated to 64KB streaming (get_file_stream / read_blob_stream)
  - WOPI, dedup, batch ZIP, file_retrieval_service consumers migrated
  - WebDAV COPY uses zero-copy dedup (copy_file)
  - Removed dead code: get_file_content, get_file_mmap, read_blob, read_blob_bytes
    from traits, impls, stubs, and mocks (18 files touched)

src/application/ports/file_ports.rs

@@ -120,9 +120,6 @@ pub trait FileRetrievalUseCase: Send + Sync + 'static {
     /// Lists files in a folder
     async fn list_files(&self, folder_id: Option<&str>) -> Result<Vec<FileDto>, DomainError>;
 
-    /// Gets file content as bytes (for small files)
-    async fn get_file_content(&self, id: &str) -> Result<Vec<u8>, DomainError>;
-
     /// Gets file content as a stream (for large files)
     async fn get_file_stream(
         &self,