chore(project): initialize project with core configuration and dependencies

- Add .gitignore and .env.example files for project setup
- Create build script for proto compilation with tonic-prost
- Generate Cargo.lock with all project dependencies
- Configure project structure and ignore patterns for development environment

main.rs

@@ -0,0 +1,75 @@
+use emailks::{
+    config::AppConfig, email::EmailSender, pb::email::v1::email_service_server::EmailServiceServer,
+    queue::EmailQueue, server::EmailServiceImpl,
+};
+use tonic::transport::Server;
+use tracing::{error, info};
+
+const DEFAULT_QUEUE_CAPACITY: usize = 1_000;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    tracing_subscriber::fmt()
+        .with_env_filter(
+            tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| "info".into()),
+        )
+        .init();
+
+    let config = AppConfig::from_env()?;
+    info!(?config.smtp.host, port = config.smtp.port, "smtp config loaded");
+
+    let sender = EmailSender::new(config.smtp)?;
+    let (queue, worker) = match config.queue_capacity {
+        Some(0) => {
+            info!("creating unbounded queue by explicit configuration");
+            EmailQueue::unbounded()
+        }
+        Some(cap) => {
+            info!(capacity = cap, "creating bounded queue");
+            EmailQueue::bounded(cap)
+        }
+        None => {
+            info!(
+                capacity = DEFAULT_QUEUE_CAPACITY,
+                "creating bounded queue with default capacity"
+            );
+            EmailQueue::bounded(DEFAULT_QUEUE_CAPACITY)
+        }
+    };
+
+    let store = queue.status_store().clone();
+    let worker_handle = worker.spawn(move |job| {
+        let s = sender.clone();
+        async move { s.send_job(&job).await }
+    });
+
+    let addr = config.listen_addr;
+    let svc = EmailServiceImpl::new(queue, store);
+
+    let (health, health_svc) = tonic_health::server::health_reporter();
+    health
+        .set_serving::<EmailServiceServer<EmailServiceImpl>>()
+        .await;
+
+    info!(%addr, "gRPC server starting");
+    Server::builder()
+        .add_service(health_svc)
+        .add_service(EmailServiceServer::new(svc))
+        .serve_with_shutdown(addr, shutdown_signal())
+        .await?;
+
+    info!("server stopped");
+
+    if let Err(e) = worker_handle.await {
+        tracing::error!(error = %e, "worker task panicked");
+    }
+
+    Ok(())
+}
+
+async fn shutdown_signal() {
+    match tokio::signal::ctrl_c().await {
+        Ok(()) => info!("shutdown signal received, draining..."),
+        Err(err) => error!(%err, "failed to install CTRL+C handler, shutting down"),
+    }
+}