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

[hogan-yuan]

What

Ports longbridge/openapi#604 to the Go SDK. Adds quote.Transport (quote.TransportWebSocket, default / quote.TransportHTTP), set with quote.WithTransport(...), config.Config.QuoteTransport or env LONGBRIDGE_QUOTE_TRANSPORT=ws|http. With TransportHTTP the 19 QuoteContext pull APIs that have a REST equivalent (StaticInfo, Quote, OptionQuote, WarrantQuote, Depth, Brokers, Participants, Trades, Intraday, Candlesticks, HistoryCandlesticksByOffset/ByDate, OptionChainExpiryDateList, WarrantIssuers, WarrantList, TradingSession, TradingDays, CapitalFlow, CapitalDistribution, CalcIndex) go over POST /quote/* instead of the quote WebSocket. Method signatures and return types are unchanged.

Why

Same motivation as the Rust PR: longbridge/longbridge-mcp#162 re-implemented every quote tool on the REST endpoints inside the MCP to get rid of its per-user WebSocket pool. That belongs in the SDK, and Go consumers should get the same switch.

How

• quote/transport.go: httpPaths maps WebSocket commands to REST paths; core.do branches on the transport. Requests are the same protobuf messages encoded with protojson (proto field names, absent sub-messages omitted); responses are decoded with protojson (DiscardUnknown, so the gateway's extra volume_str is ignored; int64-as-string and null sub-messages are handled natively).
• Lazy WebSocket: newCore no longer dials unconditionally. With TransportWebSocket it dials and fetches the profile up front exactly as before; with TransportHTTP the socket is dialed on first need (Subscribe, On* callbacks, Profile(), Subscriptions, or any command without a REST path) via core.ws(). Push handlers registered before the dial are queued and attached when it happens. Close() is a no-op if never dialed.
• quote/overnight.go aligns the one known server-side difference: REST always returns US overnight data and has no opt-out, while the WebSocket only returns it with WithEnableOvernight(true). On the HTTP path (and only there) the SDK clears OverNightQuote, filters overnight Intraday lines for US equities, and for CandlestickTradeSessionAll history queries drops OVERNIGHT_TRADE bars and tops up count/range-capped windows with offset queries (≤1000 per request, ≤8 rounds). The WebSocket path is behaviourally identical to main.
• examples/quote_http_compare calls every pull API over both transports and diffs the JSON output.

Verification

• go test ./quote/ passes (new tests: refill paging scenarios, US overnight window in EDT/EST, command→path map completeness, gateway proto-JSON decode replay, request encoding). The two failing config package tests (Test_YamlConfig / Test_TomlConfig) fail identically on main (missing fixture files) and are unrelated.
• go vet ./quote/ reports only the pre-existing copylocks warnings from util.Copy (same 8 on main).
• Canary (openapi-global.longbridge.xyz), overnight off: 30/32 cases identical between transports; the 2 remaining are the gateway error-code gap below. Production and overnight-on runs plus the full input/output report follow in a comment.

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).
2. Production /quote/* replicas are not consistent with each other (value-level differences in avg_price/volume; two consecutive REST calls can disagree while the WS is stable).
3. No REST opt-out for US overnight data (handled client-side here).

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