Restart IB Gateway before each job when it has lost IBKR's servers

On 2026-09-29 Gateway lost its connection, failed the reconnect's SSL
handshake and sat on an error dialog for 9 hours with its API port open:
clients connected, every startup request timed out, and systemd never
restarted it because java kept running.

- Broker connects with raiseSyncErrors, so a failed startup sync exits
  instead of continuing with an empty portfolio(), which rebalance would
  read as holding nothing.
- `ibkr-quant gateway` probes the Gateway under its own health_client_id.
- deploy/ensure-gateway.sh (`make gateway`) probes, waits a minute for a
  self-reconnect, then restarts ibgateway.service and waits for it.
- The trade and fills units run `make gateway` as ExecStartPre; fills
  now retries on failure like trade does.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

config.toml

@@ -2,6 +2,7 @@
 host = "127.0.0.1"
 port = 4002             # IB Gateway: paper 4002 / live 4001; TWS: paper 7497 / live 7496
 client_id = 17
+health_client_id = 18   # `ibkr-quant gateway` probe; differs so it never collides with a running job
 account = ""            # empty = the single account managed by this login
 market_data_type = 3    # 1 = live (needs subscription), 3 = delayed (free, for testing)
 allow_live = false      # refuse to connect to non-paper accounts unless true