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/core/state_sync.py

@@ -465,7 +465,6 @@ class StateSync:
 
         payload = {
             "server_mode": self._state.get("server_mode", "live"),
-            "is_mock_mode": self._state.get("is_mock_mode", False),
             "is_backtest": self._state.get("is_backtest", False),
             "tickers": self._state.get("tickers"),
             "runtime_config": self._state.get("runtime_config"),