Plan a road route for custom-route shipments (#328)

[Connor-Finn]

Part 1 of #328.

What changed

• ShipmentRoute (new table, reference role): the planned road route for a shipment on a custom route (no lane), with the stop sequence it was calculated for (stopsKey).
• ShipmentRoutePlanner, run by ShipmentRoutePlanningHandler on shipment.created / shipment.updated:
  • a lane shipment rides its lane; any route of its own is removed
  • a draft or ready custom-route shipment gets a Google Directions route through its stops in sequence, only when the stops changed
  • the provider is called off the request path and outside any transaction; SetShipmentRouteCommand stores the result and emits shipment.route_planned
  • with no Google Maps server key, planning is skipped and logged
• One effective route (ShipmentRouteRepository.findEffectiveRoute): the shipment's own route, otherwise its lane's. Checkpoints, route deviation in the ETA monitor, the new GET /api/v1/shipments/:id/route and the shipment map use it.
• Route planning is registered in the embedded (API) workers, which register their other handlers without a command bus.

Testing

• Full backend suite, tsc (backend and frontend), tenancy and boundary lints pass.
• Live against a seeded database: a lane shipment returns its lane's route and the map draws it through the new endpoint; a shipment with neither returns null; an unknown id returns 404; creating a custom-route shipment ran the planner (no server key in the test org, so no_server_key as expected). The Google call is covered by tests with it stubbed.

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