Save configured exercises to the routine draft

[rd-code-23]

Summary

• Save a configured exercise into the shared routine React Hook Form draft
• Return to the routine editor after configuration and show the updated exercise count
• Keep exercise defaults in the shared Zod contract instead of duplicating them in the UI
• Report numeric control changes back to React Hook Form

How the form works

The configuration screen uses a small local React Hook Form for the exercise being edited. Clicking Done validates that exercise with the shared contract, appends the parsed result to the parent routine form, and navigates back to the routine editor.

The shared Zod defaults make fields optional on the schema's input side because omitted or undefined values can be replaced. After parsing, those fields are guaranteed. The routine form therefore uses separate z.input and z.output types so React Hook Form accurately represents both the editable values and validated submission values.

Validation

• pnpm lint
• pnpm typecheck
• contract tests
• focused exercise configuration and routine editor tests