Update secrets and email types

- Refactor secrets module structure
- Remove unused type in email types
- Improve error handling in secrets

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/core/secrets/mod.rs

@@ -7,7 +7,6 @@ use std::env;
 use std::path::PathBuf;
 use std::sync::Arc;
 use std::sync::Arc as StdArc;
-use tokio::sync::RwLock;
 use std::sync::RwLock as StdRwLock;
 use uuid::Uuid;
 use vaultrs::client::{VaultClient, VaultClientSettingsBuilder};
@@ -147,7 +146,7 @@ impl SecretsManager {
 
         Ok(Self {
             client: Some(StdArc::new(client)),
-            cache: Arc::new(RwLock::new(HashMap::new())),
+            cache: Arc::new(StdRwLock::new(HashMap::new())),
             cache_ttl,
             enabled: true,
         })
@@ -599,18 +598,21 @@ impl SecretsManager {
     }
 
     pub async fn clear_cache(&self) {
-        self.cache.write().await.clear();
+        if let Ok(mut cache) = self.cache.write() {
+            cache.clear();
+        }
     }
 
     async fn get_cached(&self, path: &str) -> Option<HashMap<String, String>> {
-        let cache = self.cache.read().await;
+        let cache = self.cache.read().ok()?;
         cache
             .get(path)
             .and_then(|c| (c.expires_at > std::time::Instant::now()).then(|| c.data.clone()))
     }
 
     async fn cache_secret(&self, path: &str, data: HashMap<String, String>) {
-        self.cache.write().await.insert(
+        if let Ok(mut cache) = self.cache.write() {
+            cache.insert(
                 path.to_string(),
                 CachedSecret {
                     data,
@@ -619,9 +621,12 @@ impl SecretsManager {
                 },
             );
         }
+    }
 
     async fn invalidate_cache(&self, path: &str) {
-        self.cache.write().await.remove(path);
+        if let Ok(mut cache) = self.cache.write() {
+            cache.remove(path);
+        }
     }
 
     fn get_from_env(path: &str) -> Result<HashMap<String, String>> {

src/email/types.rs

@@ -394,7 +394,6 @@ impl EmailService {
         file_data: Vec<u8>,
         filename: &str,
     ) -> Result<(), String> {
-        use lettre::message::header::ContentType;
         use lettre::message::{Attachment, Body, Message, MultiPart, SinglePart};
         use lettre::transport::smtp::authentication::Credentials;
         use lettre::{SmtpTransport, Transport};