Fix SFTP path resolution and EOF handling

- Fix resolve_path() to handle non-existent files (for upload)
- Add SSH_MSG_CHANNEL_EOF handling in service loop
- Canonicalize root_dir in SftpHandler constructor
- SFTP now fully working: pwd, ls, cd, get, put operations verified

markbase-core/src/ssh_server/server.rs

@@ -345,6 +345,10 @@ fn handle_ssh_service_loop(
                 }
                 break;
             }
+            Some(&pt) if pt == PacketType::SSH_MSG_CHANNEL_EOF as u8 => {
+                info!("Received SSH_MSG_CHANNEL_EOF");
+                // EOF means client won't send more data, just acknowledge and continue
+            }
             Some(&pt) if pt == PacketType::SSH_MSG_DISCONNECT as u8 => {
                 info!("Received SSH_MSG_DISCONNECT");
                 break;