refactor: extract EmailksServer as library, thin main.rs to bootstrap-only

- Add EmailksServer / EmailksServerBuilder to lib.rs
- Expose serve() / serve_with_shutdown() for embedding
- main.rs now only handles etcd config and delegates to library

main.rs

@@ -1,12 +1,9 @@
 use emailks::{
-    config::AppConfig, email::EmailSender, etcd::{EtcdConfig, ServiceRegistry},
-    pb::email::v1::email_service_server::EmailServiceServer, queue::EmailQueue,
-    server::EmailServiceImpl,
+    config::AppConfig,
+    etcd::{EtcdConfig, ServiceRegistry},
+    EmailksServer,
 };
-use tonic::transport::Server;
-use tracing::{error, info};
-
-const DEFAULT_QUEUE_CAPACITY: usize = 1_000;
+use tracing::info;
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
@@ -19,7 +16,6 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     dotenvy::dotenv().ok();
 
-    // Phase 1: read etcd endpoints from env (required to bootstrap etcd)
     let etcd_endpoints: Vec<String> = std::env::var("ETCD_ENDPOINTS")
         .unwrap_or_else(|_| "http://localhost:2379".to_string())
         .split(',')
@@ -29,15 +25,12 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let etcd_prefix = std::env::var("ETCD_KEY_PREFIX")
         .unwrap_or_else(|_| "/appks/".to_string());
 
-    // Phase 2: connect etcd, create config overlay (etcd > env > default)
     let etcd = EtcdConfig::connect(etcd_endpoints, &etcd_prefix).await?;
     let listen_addr_str = etcd.get("EMAILKS_LISTEN_ADDR", "127.0.0.1:50051").await;
 
-    // Phase 3: register this service so other services (appks) can discover us
     let registry = ServiceRegistry::new(etcd.client(), &etcd_prefix);
     registry.register("emailks", &listen_addr_str).await?;
 
-    // Phase 4: load SMTP config — each key: etcd first, then env, then default
     let smtp_host = etcd.get("APP_SMTP_HOST", "").await;
     if smtp_host.is_empty() {
         return Err("APP_SMTP_HOST is required (set via etcd or env)".into());
@@ -68,54 +61,8 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     info!(host = %config.smtp.host, port = config.smtp.port, "smtp config loaded (etcd priority)");
 
-    let sender = EmailSender::new(config.smtp)?;
-    let (queue, worker) = match config.queue_capacity {
-        Some(0) => {
-            info!("creating unbounded queue");
-            EmailQueue::unbounded()
-        }
-        Some(cap) => {
-            info!(capacity = cap, "creating bounded queue");
-            EmailQueue::bounded(cap)
-        }
-        None => {
-            info!(capacity = DEFAULT_QUEUE_CAPACITY, "creating bounded queue (default)");
-            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");
-    }
+    let server = EmailksServer::builder().config(config).build().await?;
+    server.serve().await?;
 
     Ok(())
 }
-
-async fn shutdown_signal() {
-    match tokio::signal::ctrl_c().await {
-        Ok(()) => info!("shutdown signal received"),
-        Err(err) => error!(%err, "failed to install CTRL+C handler"),
-    }
-}