docs: add terminal color cookbook recipe

[arindamsikder]

Summary

Add a terminal-color recipe to the cookbook and note it in the unreleased changelog. Documentation only: no library behavior, dependency, configuration or version changes.

Problem

The discussion in #59 explicitly welcomes a cookbook addition rather than built-in coloring. Inserting ANSI escapes into fields before JSON serialization produces escaped JSON strings, not terminal formatting around the output.

Solution

• Show a small JsonFormatter subclass that colors the serialized console line by log level without adding color to the record or caller data.
• Disable color for redirected output or nonempty NO_COLOR, with an explicit off switch and an explanation that isatty() is not ANSI-capability detection.
• Keep a separate plain-JSON handler for ingestion. Explain that colored console output is not raw JSON and must not be merged into that stream.
• Show the machine-readable output and document unknown-level behavior.

Testing

Executed on Python 3.11 in a credential-free, network-isolated Bubblewrap environment, on both unchanged main and the proposed docs:

• python -m pytest tests -q -p no:cacheprovider --basetemp=/tmp/pytest — 221 passed on each.
• python -m black --check --diff src tests — passed.
• python -m pylint src — passed, 10/10.
• python -m mypy src tests --cache-dir /tmp/mypy-cache — passed, 14 files.
• Extracted the published Python fence verbatim into /out/terminal_color.py; Black with --config /work/pyproject.toml and mypy both passed for that snippet.
• python -m pytest /out/test_terminal_color_recipe.py -q -c /dev/null --rootdir=. -p no:cacheprovider --basetemp=/tmp/recipe — 24 passed in a local validation harness (not added to the project). Cases cover the displayed output, all five standard levels, a custom level, explicit disable, redirected/TTY output, NO_COLOR, interpolation, embedded quotes/newlines/escape data, dictionary messages, exceptions, and both handler orders. Removing the color wrapper in a sandbox-only copy produced 12 expected failures; restoring it passed all 24. The initial missing-recipe check also failed on unchanged main.
• python -m mkdocs build --site-dir /out/final-site — completed; rendered cookbook section and warning verified. Used the same compatible local docs toolchain on base and final (mkdocstrings==0.30.1, mkdocstrings-python==1.18.2, mkdocs-gen-files==0.5.0). Both builds have seven existing annotation warnings and an offline Python inventory diagnostic; this is not a warning-free build. The newer installed docs toolchain fails on unchanged configuration, so no upstream dependency change was made.
• git diff --check, added-line security scan and independent AI diff review — passed. Black reports the same target-Python warning on unchanged and final code.

Other Python/OS combinations and an interactive terminal rendering check were not run; ANSI byte output and JSON separation were checked programmatically.

Related Issue

Refs #59 — implements only the cookbook scope invited in the discussion, not a built-in color feature.

AI disclosure

Prepared, tested and independently AI-reviewed by Hermes DEV, an autonomous coding agent acting for @arindamsikder. No human pre-review is claimed.