feat(k8s): add Kubernetes Helm chart for emailks service

- Create Helm chart structure with Chart.yaml and values.yaml
- Add deployment template with container configuration and environment variables
- Implement service template for gRPC port exposure
- Add service account template with security configuration
- Include horizontal pod autoscaler template for scaling capabilities
- Add helper templates for naming and label management
- Configure SMTP settings as configurable parameters in values.yaml
- Set up resource limits and requests for container performance
- Implement liveness and readiness probes for health checks
- Add support for existing secrets and custom configurations

email_build.rs

@@ -6,6 +6,7 @@ use lettre::{
     },
     transport::smtp::{self, authentication::Credentials, extension::ClientId},
 };
+use tracing;
 
 use crate::{
     config::{SmtpConfig, SmtpTls},
@@ -105,6 +106,13 @@ pub(crate) fn build_single_attachment(
             url: att.url.clone(),
         });
     }
+    if !att.data.is_empty() && !att.url.trim().is_empty() {
+        tracing::warn!(
+            filename = att.filename,
+            url = att.url,
+            "attachment has both inline data and url; url will be ignored"
+        );
+    }
     let ct: ContentType = if att.content_type.trim().is_empty() {
         "application/octet-stream"
             .parse()
@@ -228,6 +236,9 @@ pub fn build_message_from_parts(
     }
 
     let from = resolve_sender(config, request)?;
+    if request.subject.trim().is_empty() {
+        tracing::warn!("email subject is empty — some SMTP servers may reject it");
+    }
     let mut builder = Message::builder()
         .from(from)
         .subject(request.subject.clone());