Generate `features.json`

Create a scored, reusable feature list from changes.json.

This is the triage stage of the release notes pipeline. It turns the comprehensive manifest of shipped changes into a ranked set of candidates for external communication.

Use editorial-scoring as the canonical rubric. Do not invent a different notion of importance for this step.

Purpose

changes.json answers what shipped.

features.json answers what is worth talking about, while staying schema-compatible with changes.json so the two files can be joined, diffed, and compared easily.