feature-new

Scaffold a new feature narrative document in an existing layer following the ULTRAPACK-style template extended for feature-layer architecture (principle 28). Creates docs/layers/<layer>/features/feat-NNN-<slug>.md with Design / Plan / Verify / Conclusion sections, populates layer README features table, and adds entry to feature_list.json if present. Use when: "create a new feature", "start work on feature", "scaffold feature doc", "/feature-new", "new feature in <layer>", "begin feature narrative". Auto-allocates next F-NNN ID. Do NOT use to create the layer itself or its bounded-concern KB scaffold; use /layer-new for that (a feature lives inside an already-existing layer).