[POC] Add Data Designer recipe CLI

[oliverholworthy]

Summary

This is a proof of concept for making application-level Data Designer pipelines installable and discoverable as recipes.

It adds a small recipe API, entry point discovery via data_designer.recipes, and CLI commands for listing, inspecting, validating, previewing, and running installed recipes.

Notes

• POC intended to demonstrate the shape of a recipe extension point.
• Pairs with the DataDesignerPlugins PR that exposes retrieval-sdg as a recipe.
• Focused tests cover registry behavior and CLI dispatch.

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[oliverholworthy]

Closing this older run-recipe POC as superseded by the newer split PRs:

• [POC] Support Python workflow args in CLI #612 adds the feat: support custom CLI args for Python config modules #507-style base primitive for Python workflow args on preview, create, and validate.
• [POC] Add Data Designer recipe discovery #613 layers named recipe discovery and inspection on top of that primitive.

The newer split is intended to align better with the Data Designer recipe feedback: keep executable workflow support independently reviewable, then add external recipe registration without coupling DataDesigner core to a specific recipes repository.