Migrate GET /hub from the Python proxy to a Rust handler deriving counts from
authoritative state: clubPlayers = owned PLAYER cards in Core (consumables/staff
excluded via catalog kind; may be lower than Python's profile count by the
deferred Legend instances = DIFFERENT-BY-DESIGN), auction/tradePile counts from
the durable market store via the async bridge. Fail-closed 503 on Core error;
market read failure degrades cosmetic counts to 0. Adds classify arm, handler,
ownership + integration tests; reachability tool marks hub migrated.