docs: tambah doc comment, logging, dan inline comments di semua 255 file

Meliputi:
- File-level //! doc comment: tujuan file, alur kerja, komponen utama
- Function-level /// doc comment: apa, parameter, return, flow, edge cases
- Struct/enum/trait /// doc comment: peran, field docs
- Tracing logging (tracing::info!/debug!/trace!/warn!/error!) di setiap fungsi
- Inline comments untuk variable dan branching logic penting
- Seluruh 8 crates di workspace: zesdex-backend, zesdex-cms, zesdex-entities,
  zesdex-iam, zesdex-infra, zesdex-ipc, zesdex-middleware, zesdex-utils
- Build: 0 errors, 242/242 tests passed

crates/zesdex-iam/src/domain/mod.rs

@@ -1,3 +1,16 @@
+//! Domain layer for IAM (Identity & Access Management).
+//!
+//! Pure entities, repository traits, and service traits — no infrastructure
+//! or application orchestration logic.
+//!
+//! # Sub-modules
+//!
+//! - [`oauth`] — `OAuthConfig`, `OAuthToken` entities
+//! - [`repository`] — Trait definitions: `OAuthRepository`, `SessionRepository`,
+//!   `SessionLockRepository`, `Rng`
+//! - [`service`] — Trait definitions: `OAuthService`, `SessionService`
+//! - [`session`] — `Session` entity (IAM wrapper around `zesdex_entities::Session`)
+
 pub mod oauth;
 pub mod repository;
 pub mod service;