perf: replace dyn trait objects with concrete types to eliminate vtable overhead

Remove async-trait dependency and use native Rust async fn in traits.
Replace Arc<dyn Trait> with Arc<ConcreteType> throughout the codebase
to enable monomorphization and eliminate dynamic dispatch overhead.

Key changes:
- Remove write-behind cache (no implementation existed)
- Fix should_transcode static method call
- Use ContactStorageAdapter directly instead of dyn AddressBookUseCase
- Clean up unused trait imports across services and DI

https://claude.ai/code/session_01EbAFEfyJNLRmJHmmYDX3Tt

src/interfaces/api/handlers/admin_handler.rs

@@ -14,6 +14,7 @@ use crate::application::dtos::settings_dto::{
 use crate::common::di::AppState;
 use crate::interfaces::errors::AppError;
 use std::sync::Arc;
+use crate::application::ports::auth_ports::TokenServicePort;
 
 /// Admin API routes — all require admin role.
 pub fn admin_routes() -> Router<Arc<AppState>> {