refactor: remove mock trading functionality from backend and frontend

Removes all mock price simulation features:
- Delete MockPriceManager from backend/data/
- Remove mock_mode, enable_mock, is_mock_mode flags from services
- Remove mock CLI options and config
- Remove mock mode UI components and state from frontend
- Update tests to remove mock references

Now system supports only live and backtest modes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/data/__init__.py

@@ -1,6 +1,5 @@
 # -*- coding: utf-8 -*-
 from backend.data.historical_price_manager import HistoricalPriceManager
-from backend.data.mock_price_manager import MockPriceManager
 from backend.data.polling_price_manager import PollingPriceManager
 
-__all__ = ["MockPriceManager", "PollingPriceManager", "HistoricalPriceManager"]
+__all__ = ["PollingPriceManager", "HistoricalPriceManager"]