feat: override trade tab — manual order entry with auto-registration

Backend:
- OverrideOrderRequest/Response Pydantic models with ticker, quantity, price validators
- POST /api/trading/override/order endpoint (enqueue to Redis broker queue)
- auto_register_symbol() module for untracked ticker registration via Symbol Registry
- Unit tests (17) and property-based tests (3 x 100 examples)

Frontend:
- OverrideTradePanel component (order form + positions display)
- Override tab in TradingEngine page with URL search param navigation
- Override Trade button on Trading Controls page
- useSubmitOverrideOrder mutation hook
- MSW handler and 13 component/integration tests

Steering:
- Updated steering docs for Ubuntu dev machine with nvm/Node 24

frontend/src/api/tradingHooks.ts

@@ -336,3 +336,39 @@ export function useUpdateNotificationConfig() {
     onSuccess: () => qc.invalidateQueries({ queryKey: ['notification-config'] }),
   });
 }
+
+// ---------------------------------------------------------------------------
+// Override Order (manual trade submission)
+// ---------------------------------------------------------------------------
+
+export interface OverrideOrderRequest {
+  ticker: string;
+  side: 'buy' | 'sell';
+  quantity: number;
+  order_type: 'market' | 'limit' | 'stop' | 'stop_limit';
+  limit_price?: number;
+  stop_price?: number;
+}
+
+export interface OverrideOrderResponse {
+  job_id: string;
+  status: string;
+  ticker: string;
+  side: string;
+  quantity: number;
+  auto_registered: boolean;
+}
+
+/** Submit a manual override order to the trading engine. */
+export function useSubmitOverrideOrder() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (body: OverrideOrderRequest) =>
+      apiPost<OverrideOrderResponse>('trading', '/api/trading/override/order', body),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['orders'] });
+      qc.invalidateQueries({ queryKey: ['positions'] });
+      qc.invalidateQueries({ queryKey: ['companies'] });
+    },
+  });
+}