v0.5.0 standalone challenges

All six challenge types are implemented in the portable CareerChallenges.h evaluator. Each is based on the existing four ordered checkpoint gates; no additional physical track exists.

ID	Name	Condition	Bronze/Silver/Gold target
6	Clock Hunter	One-lap time (s)	160 / 130 / 100
7	Clean Circuit	Two laps; maximum recoveries	2 / 1 / 0
8	Gate Guardian	Two ordered laps, time (s)	300 / 255 / 210
9	Lap Consistency	Three laps; slowest minus fastest (s)	24 / 15 / 8
10	Kestrel Mastery	Two laps using owned Kestrel, time (s)	320 / 275 / 230
11	Long Haul	Six ordered laps, time (s)	1100 / 950 / 800

Time targets are initial experimental balance values, not measured gameplay achievements. A player can complete a race without earning a medal if the objective is missed. Clean and precision results use the player's actual ordered-checkpoint and recovery data, never rival telemetry.

Invalid / nonfinite time or lap values, interrupted race, malformed vehicle ID, mismatched lap count, negative recovery count and wrong vehicle are rejected. Kestrel must be unlocked through in-game earned credits first.

Replay can improve a stored medal/series points, but first-completion challenge credits are paid once only. No money, external services, pay-to-win or network connection is required.

The C++20 tests validate each challenge category. Unreal physics, handling, timing and practical target difficulty still need engine/device QA.