Task: Repair the registrar composition and generate the risk_report_config surface

Close P01 and S01. risk_report_config generates no C++ protocol, handler, command unit or test, because registrar.cpp is a hand-written fan-out with nowhere to join a generated registrar, and the four per-entity and four history-provider registrar families it would join are composed nowhere.

• The composition points consume the generated registrar families, or the families are deleted with the reason recorded.
• risk_report_config generates its protocol, handler and shell command unit with a test, and every generated command answers.
• P01, S01 and W01 pass, and the subjects that exist only in TypeScript acquire a C++ counterpart.

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

Manual QA scenarios (scaffolded via compass add test_scenario) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.