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/cli/metadata/config.rs

@@ -45,7 +45,9 @@ pub fn handle_config_command(cmd: ConfigCommand) -> anyhow::Result<()> {
             let config_path = Path::new("config/markbase.toml");
 
             if !config_path.exists() {
-                println!("Configuration file not found. Run 'markbase metadata config init' first.");
+                println!(
+                    "Configuration file not found. Run 'markbase metadata config init' first."
+                );
                 return Ok(());
             }
 
@@ -61,7 +63,9 @@ pub fn handle_config_command(cmd: ConfigCommand) -> anyhow::Result<()> {
             let config_path = Path::new("config/markbase.toml");
 
             if !config_path.exists() {
-                println!("Configuration file not found. Run 'markbase metadata config init' first.");
+                println!(
+                    "Configuration file not found. Run 'markbase metadata config init' first."
+                );
                 return Ok(());
             }
 
@@ -86,7 +90,9 @@ pub fn handle_config_command(cmd: ConfigCommand) -> anyhow::Result<()> {
             let config_path = Path::new("config/markbase.toml");
 
             if !config_path.exists() {
-                println!("Configuration file not found. Run 'markbase metadata config init' first.");
+                println!(
+                    "Configuration file not found. Run 'markbase metadata config init' first."
+                );
                 return Ok(());
             }
 
@@ -115,4 +121,4 @@ fn show_section(config: &crate::config::MarkBaseConfig, section: &str) {
         "logging" => println!("{}", toml::to_string_pretty(&config.logging).unwrap()),
         _ => println!("Invalid section: {}. Valid sections: server, postgresql, authentication, test, logging", section),
     }
-}
+}