test: expand coverage across rover, pskr, valkey, skewt, scores
- Rover.Compute: road/prominence/clearance/clutter/canopy tests (90%)
- Rover.Prominence: full unit test suite with mock elev_lookup (100%)
- Rover.Elevation: dedup + multi-tile tests (44%)
- Rover.LinkMargin: edge cases, negative scores, all modes (57%)
- Rover.Location: changeset validation + statuses/0 (100%)
- RoverPlanning.Path: changeset validation + statuses/0 (67%)
- Pskr.FeatureBin: changeset validation (100%)
- Pskr.Mqtt: QoS reject, unknown type, varint overflow, ping/disconnect (97%)
- Valkey: not-configured error paths, empty guards (55%)
- ScoresController: bad params, time format, missing band tests (81%)
- SkewtLive: info/no-profiles state, loading states (29%)