[Viviiii16]

Closes #15

What changed

• Backend (GET /rides/{id}/route):** Added approach_duration_s to RouteOut and populated it from ctx.routes.estimate while the driver is on the way (driver_assigned).
• Backend (driver:location events):** Added throttled road-route ETA calculation (ETA_INTERVAL_S = 15.0) in backend/app/services/locations.py so approach_duration_s is sent to the rider roughly every 15 seconds without recalculating on every raw GPS ping.
• Rider App (mobile/):** Updated useRideRoute to consume live approach_duration_s updates from driver:location events and updated riderStatusText / RiderRide screen to display "Arriving in N min" and switch to "Driver has arrived" upon arrival.

Testing

• Extended backend/tests/test_api.py (test_full_ride_lifecycle and test_routes_follow_the_roads) to verify approach_duration_s on GET /rides/{id}/route and 15-second throttling on driver:location.
• Added unit tests in mobile/src/lib/__tests__/format.test.ts for riderStatusText.
• Ran python test_all.py --quick and verified with python demo.py.

closes #15