Add src/output/ module with three renderers:
- table.rs: render_table() using comfy-table with dynamic column sizing
- json.rs: render_json<T: Serialize>() using serde_json pretty-print
- xml.rs: render_xml_rows() with XML-escaped headers and values
Each renderer has unit tests (17 new tests total); total test count: 79 passing, 0 clippy warnings.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>