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

filetree-rocksdb/src/lib.rs

@@ -312,9 +312,9 @@ impl FileTreeRocksDB {
         label: &str,
         file_uuid: &str,
         sha256: Option<&str>,
-        original_name: &str,
+        _original_name: &str,
         file_size: Option<i64>,
-        mime_type: Option<&str>,
+        _mime_type: Option<&str>,
         parent_id: Option<&str>,
     ) -> FileNode {
         FileNode {