fix(zerogpu): persist quota ledger so a restart stops claiming phantom minutes

fix(quota): expire stale quota_exhausted_observed flag via TTL

feat(telemetry): record completion tokens for GPU throughput metric

fix(telemetry): detect cold start inside ZeroGPU worker body

fix(telemetry): gpu_tracked_call must open lease before GPU body

feat(telemetry): ZeroGPU quota accounting in /v1/gpu/status (GOAL.md M3 line 54)