Add rate limiter (50/s + 5/s historical), symbol mapper, order builders,
account queries, market data subscriptions, and high-level CTraderClient
that orchestrates the full connect/auth/symbol-load lifecycle.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
HTTP OAuth2 flow (auth code exchange + refresh) via reqwest, plus
protobuf-level two-phase auth (ApplicationAuth → AccountAuth) over
the TCP connection. Error extraction from OA error responses.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>