docs: add guide for optional output-format dependencies and strict JSON consumer validation

[bogusdeck]

Summary

This PR addresses two documentation issues:

1. docs: add a focused guide for optional output-format dependencies #346: Add a guide for optional output-format dependencies.
2. docs: document strict JSON consumer validation with Node #345: Document strict JSON consumer validation with Node.js.

Changes

• docs/output-contracts.md

  • Added a table documenting optional output-format dependencies, including yaml and rich.

• docs/json-contracts.md

  • Added a section explaining how to validate base CLI JSON and NDJSON output using Node.js's JSON.parse.

Notes

Both changes are documentation-only and follow the acceptance criteria defined in their respective issues.

[codeforester]

Cleanup: the new "Contract fixtures and validator" section is a near-verbatim duplicate of the paragraph already present ~25 lines above it in the same file (both describe CI validating fixtures against packaged schemas via a Python validator and a Node.js reader). Consider merging to avoid having to update the same claim in two places.

[codeforester]

Doc accuracy: this table says a missing PyYAML surfaces a raw ImportError: No module named 'yaml', but the code never lets that propagate — require_yaml() (lib/python/base_cli/_dependencies.py) catches ImportError and re-raises a RuntimeError with an actionable install hint, which the caller wraps into OutputFormatError. A user grepping logs for the documented string won't find it, and the doc omits the actual (more useful) message the CLI produces.