[Amey-Bhavsar]

Follow-up for #4 addressing review feedback:

1. **Unified Distance and ETA Source**:
   - Added `pickup_estimate` to `EtaProvider`, `RouterEta`, and     
   `StraightLineEta` in `matching/eta.py`.
   - Updated `RouteService.pickup_estimate` in
   `backend/app/services/routes.py` so that distance and ETA both   
   come from the road route when roads are loaded (`RouterEta`), and
   from straight-line when not (`StraightLineEta`).
2. **Offer Endpoint Assertions and Dedicated Test**:
   - Restored the `/drivers/me/offer` assertion in
   `test_full_ride_lifecycle`.
   - Added dedicated `test_driver_offer_endpoint` in
   `backend/tests/test_api.py`.
3. **Unit Tests**:
   - Added `test_pickup_estimate_uses_road_distance` in
   `tests/test_matching.py` ensuring road distance (~7.1 km across
   bridge) is returned instead of straight-line distance (~780 m).