feat(gateway): the 5 core gateway routes wired into the router
- src/gateway/routes.rs: /search /schema /call /batch /subscribe
- SSE projection: data frames per event, error event terminates,
internal/unknown ops -> NOT_FOUND, query-op -> INVALID_OPERATION_TYPE
- /search + /schema ACL-filtered via services/list + services/schema
discovery handlers; /batch ordered per-item envelope JSON
- gateway_router() merged into HttpAdapter's router under the shared
bearer-auth route layer; decoy remains the fallback
- adapted to alkcall 0.1.1: OperationType::Sub, envelope error by value
Verified: cargo test (71 lib tests), clippy -D warnings, fmt.