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/config/mod.rs

@@ -8,6 +8,7 @@ pub use web::*;
 
 /// Unified application configuration
 #[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Default)]
 pub struct AppConfig {
     #[serde(default)]
     pub web: WebSection,
@@ -154,13 +155,19 @@ impl AppConfig {
             self.web.host = v;
         }
         if let Ok(v) = std::env::var("MB_WEB_PORT") {
-            if let Ok(p) = v.parse() { self.web.port = p; }
+            if let Ok(p) = v.parse() {
+                self.web.port = p;
+            }
         }
         if let Ok(v) = std::env::var("MB_SSH_PORT") {
-            if let Ok(p) = v.parse() { self.ssh.port = p; }
+            if let Ok(p) = v.parse() {
+                self.ssh.port = p;
+            }
         }
         if let Ok(v) = std::env::var("MB_SFTP_PORT") {
-            if let Ok(p) = v.parse() { self.sftp.port = p; }
+            if let Ok(p) = v.parse() {
+                self.sftp.port = p;
+            }
         }
         if let Ok(v) = std::env::var("MB_S3_ENABLED") {
             self.s3.enabled = v == "true" || v == "1";
@@ -172,16 +179,6 @@ impl AppConfig {
     }
 }
 
-impl Default for AppConfig {
-    fn default() -> Self {
-        Self {
-            web: WebSection::default(),
-            s3: S3Section::default(),
-            sftp: SftpSection::default(),
-            ssh: SshSection::default(),
-        }
-    }
-}
 
 #[cfg(test)]
 mod tests {

markbase-core/src/config/web.rs

@@ -323,11 +323,15 @@ impl MarkBaseConfig {
         }
 
         if self.authentication.default_user.is_empty() {
-            return Err(anyhow::anyhow!("authentication.default_user cannot be empty"));
+            return Err(anyhow::anyhow!(
+                "authentication.default_user cannot be empty"
+            ));
         }
 
         if self.authentication.default_password.is_empty() {
-            return Err(anyhow::anyhow!("authentication.default_password cannot be empty"));
+            return Err(anyhow::anyhow!(
+                "authentication.default_password cannot be empty"
+            ));
         }
 
         if self.authentication.max_sessions_per_user == 0 {