Add custom notification trade size threshold settings on Dashboard

[mx57]

Implemented minimum USDT trade size threshold settings (realtime_min_trade_size) on both Dashboard.cshtml and Settings.cshtml. The trade size filter suppresses visual pop-up toasts and synthesized sound notifications for trades with total cost (Amount * Price) below the configured USDT threshold. All settings persist in localStorage and synchronize across UI tabs.

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PR created automatically by Jules for task 8182642575343237458 started by @mx57

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