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/gateway_server.py

@@ -130,10 +130,8 @@ async def run_gateway(
     end_date = bootstrap.get("end_date")
     enable_memory = bootstrap.get("enable_memory", False)
     poll_interval = int(bootstrap.get("poll_interval", 10))
-    enable_mock = bootstrap.get("enable_mock", False)
 
     is_backtest = mode == "backtest"
-    is_mock = enable_mock or mode == "mock" or (not is_backtest and os.getenv("MOCK_MODE", "false").lower() == "true")
 
     logger.info(f"[Gateway Server] Starting run {run_id} on port {port}")
 
@@ -152,9 +150,8 @@ async def run_gateway(
             market_service = MarketService(
                 tickers=tickers,
                 poll_interval=poll_interval,
-                mock_mode=is_mock and not is_backtest,
                 backtest_mode=is_backtest,
-                api_key=os.getenv("FINNHUB_API_KEY") if not is_mock and not is_backtest else None,
+                api_key=os.getenv("FINNHUB_API_KEY") if not is_backtest else None,
                 backtest_start_date=start_date if is_backtest else None,
                 backtest_end_date=end_date if is_backtest else None,
             )
@@ -247,7 +244,6 @@ async def run_gateway(
                 scheduler_callback=scheduler_callback,
                 config={
                     "mode": mode,
-                    "mock_mode": is_mock,
                     "backtest_mode": is_backtest,
                     "tickers": tickers,
                     "config_name": run_id,