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_cli.py

@@ -34,7 +34,6 @@ def test_live_runs_incremental_market_store_update_before_start(monkeypatch, tmp
     monkeypatch.setattr(cli.subprocess, "run", fake_run)
 
     cli.live(
-        mock=False,
         config_name="smoke_fullstack",
         host="0.0.0.0",
         port=8765,