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

tests/config_tests.rs

@@ -0,0 +1,135 @@
+use emailks::config::{AppConfig, SmtpTls};
+use emailks::error::ConfigError;
+use std::sync::Mutex;
+use std::time::Duration;
+
+/// Serialize tests that mutate process-wide environment variables.
+static TEST_MUTEX: Mutex<()> = Mutex::new(());
+
+macro_rules! set_env {
+    ($k:expr, $v:expr) => {
+        unsafe { std::env::set_var($k, $v) }
+    };
+}
+macro_rules! rm_env {
+    ($k:expr) => {
+        unsafe { std::env::remove_var($k) }
+    };
+}
+
+fn clear_smtp_env() {
+    for var in &[
+        "APP_SMTP_HOST",
+        "APP_SMTP_PORT",
+        "APP_SMTP_USERNAME",
+        "APP_SMTP_PASSWORD",
+        "APP_SMTP_FROM_EMAIL",
+        "APP_SMTP_FROM_NAME",
+        "APP_SMTP_REPLY_TO",
+        "APP_SMTP_TLS",
+        "APP_SMTP_TIMEOUT_SECS",
+        "APP_SMTP_HELO_NAME",
+        "APP_SMTP_ALLOW_REQUEST_FROM",
+        "APP_SMTP_LISTEN_ADDR",
+        "APP_SMTP_QUEUE_CAPACITY",
+    ] {
+        rm_env!(var);
+    }
+}
+
+#[test]
+fn parse_smtp_config_full() {
+    let _guard = TEST_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
+    clear_smtp_env();
+    set_env!("APP_SMTP_HOST", "smtp.test.com");
+    set_env!("APP_SMTP_PORT", "465");
+    set_env!("APP_SMTP_USERNAME", "user");
+    set_env!("APP_SMTP_PASSWORD", "pass");
+    set_env!("APP_SMTP_FROM_EMAIL", "from@test.com");
+    set_env!("APP_SMTP_FROM_NAME", "Test");
+    set_env!("APP_SMTP_REPLY_TO", "reply@test.com");
+    set_env!("APP_SMTP_TLS", "tls");
+    set_env!("APP_SMTP_TIMEOUT_SECS", "60");
+    set_env!("APP_SMTP_HELO_NAME", "helo.test.com");
+
+    let s = &AppConfig::from_env().unwrap().smtp;
+    assert_eq!(s.host, "smtp.test.com");
+    assert_eq!(s.port, 465);
+    assert_eq!(s.username.as_deref(), Some("user"));
+    assert_eq!(s.password.as_deref(), Some("pass"));
+    assert_eq!(s.from_email.as_deref(), Some("from@test.com"));
+    assert_eq!(s.from_name.as_deref(), Some("Test"));
+    assert_eq!(s.reply_to.as_deref(), Some("reply@test.com"));
+    assert_eq!(s.tls, SmtpTls::Tls);
+    assert_eq!(s.timeout, Duration::from_secs(60));
+    assert_eq!(s.helo_name.as_deref(), Some("helo.test.com"));
+    assert!(!s.allow_request_from);
+}
+
+#[test]
+fn parse_smtp_config_minimal() {
+    let _guard = TEST_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
+    clear_smtp_env();
+    set_env!("APP_SMTP_HOST", "smtp.test.com");
+
+    let s = &AppConfig::from_env().unwrap().smtp;
+    assert_eq!(s.host, "smtp.test.com");
+    assert_eq!(s.port, 587);
+    assert_eq!(s.tls, SmtpTls::StartTls);
+    assert_eq!(s.timeout, Duration::from_secs(30));
+    assert!(s.username.is_none());
+    assert_eq!(
+        AppConfig::from_env().unwrap().listen_addr.to_string(),
+        "127.0.0.1:50051"
+    );
+}
+
+#[test]
+fn missing_host_is_error() {
+    let _guard = TEST_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
+    clear_smtp_env();
+    let err = AppConfig::from_env().unwrap_err();
+    assert!(matches!(err, ConfigError::MissingEnv { name: "HOST" }));
+}
+
+#[test]
+fn tls_variants() {
+    let _guard = TEST_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
+    clear_smtp_env();
+    set_env!("APP_SMTP_HOST", "h");
+    for (value, expected) in [
+        ("none", SmtpTls::None),
+        ("false", SmtpTls::None),
+        ("starttls", SmtpTls::StartTls),
+        ("start_tls", SmtpTls::StartTls),
+        ("tls", SmtpTls::Tls),
+        ("ssl", SmtpTls::Tls),
+    ] {
+        set_env!("APP_SMTP_TLS", value);
+        assert_eq!(AppConfig::from_env().unwrap().smtp.tls, expected);
+    }
+}
+
+#[test]
+fn invalid_port_is_error() {
+    let _guard = TEST_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
+    clear_smtp_env();
+    set_env!("APP_SMTP_HOST", "h");
+    set_env!("APP_SMTP_PORT", "0");
+    assert!(matches!(
+        AppConfig::from_env().unwrap_err(),
+        ConfigError::InvalidEnv { name: "PORT", .. }
+    ));
+}
+
+#[test]
+fn queue_capacity_parsing() {
+    let _guard = TEST_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
+    clear_smtp_env();
+    set_env!("APP_SMTP_HOST", "h");
+    set_env!("APP_SMTP_QUEUE_CAPACITY", "100");
+    assert_eq!(AppConfig::from_env().unwrap().queue_capacity, Some(100));
+
+    rm_env!("APP_SMTP_QUEUE_CAPACITY");
+    assert_eq!(AppConfig::from_env().unwrap().queue_capacity, None);
+}