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

.kiro/steering/project-context.md

@@ -15,10 +15,11 @@ Three-layer signal aggregation engine:
 - Seed script: `python -m services.symbol_registry.seed`
 
 ## Local Dev Environment
-- NixOS dev environment, Python 3.12
+- Ubuntu dev machine, Python 3.12
 - Virtual environment at `.venv/` — always use it for Python commands
-- For tools not in `.venv/` (like `ruff`, `gh`), use `nix-shell -p <pkg> --run "<cmd>"`
-- Node.js 24 for frontend (`frontend/` directory)
+- Node.js 24 via nvm — always load nvm before running Node/npm commands:
+  `export NVM_DIR="$HOME/.nvm" && [ -s "$NVM_DIR/nvm.sh" ] && . "$NVM_DIR/nvm.sh" && nvm use 24`
+- For tools not in `.venv/` (like `ruff`, `gh`), install via pip or apt as needed
 - Docker available locally for image builds (but let CI handle pushes)
 
 ## Live Endpoints
@@ -44,7 +45,7 @@ Three-layer signal aggregation engine:
 - Superset image: `docker/Dockerfile.superset` (apache/superset + trino + psycopg2)
 - Python service images: `docker/Dockerfile` with `SERVICE_CMD` build arg
 - Let CI handle image builds and pushes — do NOT manually `docker build && docker push`
-- Check CI status: `nix-shell -p gh --run "gh run list -L 3"`
+- Check CI status: `gh run list -L 3`
 
 ## Deployment Scripts
 - `~/sources/kube/stonks-oracle/runmefirst.sh` — full deploy: DB setup, migrations, Helm install, rolling restart (runs from gremlin-1 at 192.168.42.254 where secrets are available)