feat(gate): complete Gate.io exchange integration with trader refactoring

Gate.io Integration:
- Add Gate trader with full Trader interface implementation
- Add order_sync.go for background trade synchronization
- Fix quantity display (convert contracts to actual tokens via quanto_multiplier)
- Fix fill price return in OpenLong/OpenShort/CloseLong/CloseShort
- Add Gate-specific CoinAnk K-line data source support
- Add Gate to supported exchanges in frontend and backend
- Add Gate/KuCoin logo SVG icons

Trader Package Refactoring:
- Move exchange-specific code into subdirectories (binance/, bybit/, okx/, bitget/, hyperliquid/, aster/, lighter/, gate/)
- Create types/ package for shared types to avoid circular dependencies
- Move TraderTestSuite to trader/testutil package to avoid import cycles
- Update market.GetWithExchange to support exchange-specific data

go.sum

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+github.com/antihax/optional v1.0.0 h1:xK2lYat7ZLaVVcIuj82J8kIro4V6kDe0AUDFboUCwcg=
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@@ -68,6 +70,8 @@ github.com/ferranbt/fastssz v0.1.4 h1:OCDB+dYDEQDvAgtAGnTSidK1Pe2tW3nFV40XyMkTeD
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+github.com/gateio/gateapi-go/v6 v6.104.3 h1:JQ2+s1pG4bL+JeLQyGy9c7YLr7hxRI8g7vkAuQYl75k=
+github.com/gateio/gateapi-go/v6 v6.104.3/go.mod h1:racCcjrdyOUbRDO5eCUGUiyDPrF/ZmwBj/bupPZTVLY=
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