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/tests/test_runtime_service_app.py

@@ -310,7 +310,6 @@ def test_start_runtime_restore_reuses_historical_run_id(monkeypatch, tmp_path):
                         "enable_memory": False,
                         "mode": "live",
                         "poll_interval": 10,
-                        "enable_mock": False,
                     },
                 }
             }