Expand one capability area from .gener8v/prd.md into a functional specification with atomic, testable [PREFIX]-REQ-XXX requirements, behaviors, edge cases and open questions under .gener8v/specifications/. Use when a PRD capability area needs elaboration before constraints, technical design or tickets, or a change brief still marks an area as pending specification, such as 'spec out the search area' or 'write the requirements for billing'. Not for the whole product (planning) or work items (ticket-breakdown).
