P1 solo-router rebind: adopt Class-S -> solo-mars / Class-A -> full-team as default dispatch (bs-mr8o7w73qz4)

Rebind the Lean Lane Class-S/Class-A gate as the solo-vs-full-team router per closed brainstorm bs-mr8o7w73qz4. Class-S (single-file AND reversible AND one-owner AND security-inert) -> solo-mars-cc default; Class-A (authz/scope/predicate/RLS/auth/email/schema, or large feature/refactor) -> full team. solo takes NEW Class-S WIs; coder/db/audit keep in-flight + Class-A. PM reflex flips to 'any reason NOT solo?'. Rung 0 of the graduated cutover.