Implements src/server/gateway_routes.rs: POST /call, GET /search, GET /schema,
POST /batch, POST /subscribe (SSE). All delegate to GatewayDispatch::invoke; auth
via ResolvedIdentity extractor; errors mapped via call_error_to_http_response
(identity-aware 401/403 split). Internal ops → 404. /schema adds ACL pre-check.
/subscribe projects ResponseEnvelope as SSE. /batch loops over invoke. Wired real
handlers into adapter.rs replacing placeholder 501s. 157 tests pass.
Note: /subscribe SSE completes after single event (registry invoke returns single
ResponseEnvelope, no streaming handler yet — research §6 OQ#5).
# Conflicts:
# crates/alknet-http/src/server/adapter.rs