feat(quote): add QuoteTransport to serve quote pull APIs over HTTP

[hogan-yuan]

What

Adds Config::quote_transport(QuoteTransport::{WebSocket, Http}) (env LONGBRIDGE_QUOTE_TRANSPORT=ws|http, default WebSocket). With Http, the 19 QuoteContext pull APIs that have a REST equivalent (static_info, quote, option_quote, warrant_quote, depth, brokers, participants, trades, intraday, candlesticks, history_candlesticks_by_offset/by_date, option_chain_expiry_date_list, warrant_issuers, warrant_list, trading_session, trading_days, capital_flow, capital_distribution, calc_indexes) go over POST /quote/* instead of the quote WebSocket. A process that only pulls data never opens a WebSocket connection. Public method signatures and return types are unchanged.

The option is exposed in all six layers (Rust, C, C++, Java, Node.js, Python), mirroring PushCandlestickMode.

Why

longbridge/longbridge-mcp#162 re-implemented every quote tool on top of the REST endpoints inside the MCP (per-tool JSON reshaping) to get rid of its per-user WebSocket pool. That logic belongs in the SDK: one switch in QuoteContext::request, and every SDK consumer (MCP, CLI, …) gets it with identical types.

How

• rust/src/quote/cmd_code.rs::http_path maps WS command codes to REST paths; QuoteContext::request / request_without_body branch on the transport. The request is the same prost message serialised as JSON (nulls stripped); the response is decoded into the same prost message by rust/src/quote/http_json.rs, a lenient serde deserializer (int64-as-string, omitted/null → default, camelCase keys, unknown fields ignored), so all existing TryFrom conversions are reused.
• rust/src/quote/overnight.rs aligns the one known server-side difference: REST always returns US overnight data and has no opt-out, while the WS only returns it when enable_overnight is set. On the HTTP path (and only there) the SDK strips overnight_quote, filters overnight intraday lines for US equities, drops OvernightTrade candlesticks and tops up count/range-capped candlestick windows with offset queries (≤1000 per request, ≤8 rounds). The WebSocket path is byte-identical to main.
• examples/rust/quote_http_compare calls every pull API over both transports and diffs the results.

Verification

Report with every call's request/response and WS-vs-HTTP diff (canary + production, overnight on/off): https://v.longbridge-inc.com/p/zhanghong.yuan/quote-http-传输验证

• Canary: 31/33 cases identical in both modes; the 2 remaining are the gateway error-code gap below.
• Production: all cases structurally identical; the value-level differences are a backend issue (two consecutive REST calls disagree with each other while the WS is stable — different /quote/* replicas serve different data).
• cargo test -p longbridge --lib quote:: 14/14; cargo clippy --all --all-features adds no warnings; cargo +nightly fmt --all.
• Two rounds of independent full-branch review; all blockers/should-fix findings addressed before the final runs.

Known gateway gaps (not fixable in the SDK)

1. REST reports business errors as 500 internal server error instead of passing the code through (WS: 301600, 301604, 301607). Callers that branch on error codes will not work over HTTP until this is fixed.
2. Production /quote/* data is not consistent across replicas (see report).
3. No REST opt-out for US overnight data (handled client-side here).

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