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/services/gateway.py

@@ -111,7 +111,6 @@ class Gateway:
             host=host,
             port=port,
             poll_interval=self.config.get("poll_interval", 10),
-            mock=self.config.get("mock_mode", False),
             tickers=self.config.get("tickers", []),
             initial_cash=self.storage.initial_cash,
             start_date=self._backtest_start_date or "",
@@ -125,10 +124,6 @@ class Gateway:
         self.state_sync.update_state("status", "initializing")
         self.state_sync.update_state("server_mode", self.mode)
         self.state_sync.update_state("is_backtest", self.is_backtest)
-        self.state_sync.update_state(
-            "is_mock_mode",
-            self.config.get("mock_mode", False),
-        )
         self.state_sync.update_state("tickers", self.config.get("tickers", []))
         self.state_sync.update_state(
             "runtime_config",
@@ -545,13 +540,13 @@ class Gateway:
         websocket: ServerConnection,
         data: Dict[str, Any],
     ) -> None:
-        """Run one live/mock trading cycle on demand."""
+        """Run one live trading cycle on demand."""
         if self.is_backtest:
             await websocket.send(
                 json.dumps(
                     {
                         "type": "error",
-                        "message": "Manual trigger is only available in live/mock mode.",
+                        "message": "Manual trigger is only available in live mode.",
                     },
                     ensure_ascii=False,
                 ),