spec-approach

Add a refined ## Approach section to an existing feature spec.md before TDD executes it. Reads the spec, explores the codebase to ground the approach in real modules and patterns, proposes 2–3 alternatives when they exist, validates with the user, then appends ## Approach to the same spec file. Trigger after interview-to-spec for non-trivial features when the user says "plan the approach", "spec the implementation",…