Document Typer CLI migration decision

[peetmate]

Summary

Finalize issue #34 as an evaluation outcome rather than a broad rewrite. This PR turns the existing Typer prototype note into an explicit decision memo and updates the README to document the current migration stance.

Problem / Motivation

Issue #34 asked for evaluation first, not automatic migration. The repo already had:

• a live Typer prototype on climate-toolkit-climatology
• compatibility-preserving main() entrypoint strategy
• tests around help behavior and fallback behavior

But decision evidence was scattered. This PR makes the conclusion explicit so we can close the issue cleanly.

Scope

• In scope:
  • upgrade analysis/issues/issue_34_typer_prototype_note.md into a decision memo
  • document backward-compatibility strategy
  • document current recommendation in README
• Out of scope:
  • migrating additional CLIs
  • changing console-script entry points
  • changing Typer prototype implementation itself

Implementation Notes

• analysis/issues/issue_34_typer_prototype_note.md
  • reframed as evaluation decision memo
  • added evidence from issue #68 fallback work
  • added explicit compatibility rules and migration gates
  • added clear decision: no broad rewrite yet; gradual adoption only
• README.md
  • added one-line public note describing current CLI migration policy

Data / Access / Runtime Notes

• No runtime behavior changed
• No auth behavior changed
• No dataset behavior changed
• This is documentation / decision-record work only

Testing

• Commands run:
  • .venv/bin/python -m pytest -q tests/test_packaging_metadata.py tests/test_package_import_hygiene.py tests/test_climatology_typer_cli.py
• Result:
  • 20 passed, 61 subtests passed
• Not tested:
  • no live runtime change to test beyond existing CLI prototype tests

Reviewer Guidance

Review mainly for correctness of stated decision and consistency with current repo state:

• analysis/issues/issue_34_typer_prototype_note.md
• README.md

Related Issues

• Closes Evaluate migration of CLI surface to Typer without breaking current entry points #34
• References Climatology failed to return plots and failed to returns data for some datasets #68 as follow-up evidence on Typer dependency/fallback risk

Checklist

• I reviewed my own diff for unrelated changes.
• I used a dedicated branch for this work.
• I added or updated tests where needed.
• I documented any auth, data, cache, or runtime implications.
• I included reviewer test steps or validation notes.
• I linked the relevant issue(s).