v4.0.0

Rides that find no free driver no longer fail on the first pass. The request path is now a Processor API node with a changelogged pending-retries store and a wall-clock punctuator: attempt n waits n times the base backoff (0 s, 5 s, 15 s by default), each pass appends ride.retry to the trip timeline, and only the last failure moves the row to UNMATCHED and publishes RideUnmatched with the attempt count. The pending set follows the task to the standby replica through the changelog. Covered by TopologyTestDriver tests with a mocked wall clock and a Testcontainers scenario where a driver appears after the first pass. 51 unit tests and 14 integration tests.