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

Cargo.lock

@@ -129,17 +129,6 @@ dependencies = [
  "syn",
 ]
 
-[[package]]
-name = "async-trait"
-version = "0.1.89"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9035ad2d096bed7955a320ee7e2230574d28fd3c3a0f186cbea1ff3c7eed5dbb"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn",
-]
-
 [[package]]
 name = "async_zip"
 version = "0.0.18"
@@ -1819,7 +1808,6 @@ dependencies = [
  "argon2",
  "async-compression",
  "async-stream",
- "async-trait",
  "async_zip",
  "axum",
  "base64",