Fix code quality: trailing whitespace, unused imports, clippy warnings

- Fix trailing whitespace in kex.rs and s3.rs
- Add missing KexProposal import in kex_complete.rs
- Auto-fix clippy warnings across all crates
- All 153 tests pass

markbase-core/src/auth.rs

@@ -5,7 +5,7 @@ use std::collections::HashMap;
 use std::sync::{Arc, Mutex};
 use uuid::Uuid;
 
-use crate::provider::{DataProvider, ProviderError};
+use crate::provider::DataProvider;
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct User {
@@ -71,6 +71,12 @@ pub struct AuthState {
     pub provider: Option<Arc<dyn DataProvider>>,
 }
 
+impl Default for AuthState {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl AuthState {
     pub fn new() -> Self {
         let mut users = HashMap::new();
@@ -284,7 +290,12 @@ impl AuthState {
         }
     }
 
-    fn login_with_provider(&self, provider: &dyn DataProvider, username: &str, password: &str) -> Option<LoginResponse> {
+    fn login_with_provider(
+        &self,
+        provider: &dyn DataProvider,
+        username: &str,
+        password: &str,
+    ) -> Option<LoginResponse> {
         match provider.get_user(username) {
             Ok(Some(user)) => {
                 if user.status != 1 {