TradeAutonom Exchange-Gateway: ex-nado

Multi-tenant Cloudflare Container that hosts the Python NadoClient
for every enrolled user (idFromName('singleton')).  Implements the
unified /v1/* API spec from docs/v2-exchange-gateway-architecture.md.

Requests to /v1/* and /internal/* require a valid X-Internal-Token
header matching the V2_SHARED_TOKEN secret AND an X-User-Id header
naming the target user slot.

Typical usage is indirect: user-v2 / user-v2-fr / user-v2-dna bot
containers call this gateway via the HttpGatewayClient in
app/exchange_clients/http_gateway.py.