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/main.rs

@@ -1,12 +1,12 @@
-use markbase_core::cli::Cli;
 use clap::Parser;
+use markbase_core::cli::Cli;
 
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
     env_logger::Builder::from_default_env()
         .filter_level(log::LevelFilter::Info)
         .init();
-    
+
     let cli = Cli::parse();
 
     match cli.command {
@@ -25,4 +25,4 @@ async fn main() -> anyhow::Result<()> {
     }
 
     Ok(())
-}
+}