refactor(harness): derive feature template, types, and validator from one schema

Parent: #384 (P1-5).

## Scope
Use one feature schema to derive or validate the JSON template, TypeScript type, and validator.

## Acceptance
- spec_ref, depends_on, points and all required fields are consistent everywhere.
- Parity tests fail when template/type/validator drift.
- Existing feature lists remain valid or receive an explicit migration.

Delivery discipline: one issue, one worker branch, one PR.

Start by reading parent issue #384, then locate the feature schema, JSON template, TypeScript type, validator, and parity tests named in the scope. Confirm how spec_ref, depends_on, points, and required fields are represented, then ensure drift is detected and existing feature lists remain valid or have an explicit migration.

Written by the indexing model from the issue text.