feat(api): implement user authentication and registration endpoints

- Add main application logic in `api/src/main.rs` to initialize server, database, and services.
- Create authentication routes in `api/src/routes/auth.rs` for login, register, logout, and user info retrieval.
- Implement configuration route in `api/src/routes/config.rs` to expose application settings.
- Define application state management in `api/src/state.rs` to share user service and configuration.
- Set up Docker Compose configuration in `compose.yml` for backend, worker, and database services.
- Establish domain logic in `domain` crate with user entities, repositories, and services.
- Implement SQLite user repository in `infra/src/user_repository.rs` for user data persistence.
- Create database migration handling in `infra/src/db.rs` and session store in `infra/src/session_store.rs`.
- Add necessary dependencies and features in `Cargo.toml` files for both `domain` and `infra` crates.

api/src/dto.rs

@@ -0,0 +1,42 @@
+//! Request and Response DTOs
+//!
+//! Data Transfer Objects for the API.
+
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+use validator::Validate;
+
+/// Login request
+#[derive(Debug, Deserialize, Validate)]
+pub struct LoginRequest {
+    #[validate(email(message = "Invalid email format"))]
+    pub email: String,
+
+    #[validate(length(min = 6, message = "Password must be at least 6 characters"))]
+    pub password: String,
+}
+
+/// Register request
+#[derive(Debug, Deserialize, Validate)]
+pub struct RegisterRequest {
+    #[validate(email(message = "Invalid email format"))]
+    pub email: String,
+
+    #[validate(length(min = 6, message = "Password must be at least 6 characters"))]
+    pub password: String,
+}
+
+/// User response DTO
+#[derive(Debug, Serialize)]
+pub struct UserResponse {
+    pub id: Uuid,
+    pub email: String,
+    pub created_at: DateTime<Utc>,
+}
+
+/// System configuration response
+#[derive(Debug, Serialize)]
+pub struct ConfigResponse {
+    pub allow_registration: bool,
+}