feat(transform): add auto-mapping and command chaining

Introduces two key features to improve the transformation workflow:

- Automatic Column Mapping: The column map is now optional. If omitted,
  columns are automatically mapped from the source file's headers
  (e.g., CSV headers or JSON keys).

- Command Chaining: A new result processor allows multiple commands
  to be invoked in a single sequence. The output of one command is
  passed internally to the next, enabling workflows like:
  `... transform read-csv input.csv write-file output.csv`