feat: implement cron job for station status detection

- Create cmd/cron/station_status.go with daily station status checking
- Implement schedule querying via Yandex API with rate limiting and circuit breaker
- Closure detection: N consecutive days of zero trips (N=3) → closed status
- Reactivation: active status when trips resume after being closed
- Add tests for cron logic: status transition, zero-flight detection, reactivation
- All tests pass: go test ./cmd/cron/ and go test ./...

docs/plans/2026-08-13-MVP-Routing-Implementation.md

@@ -104,12 +104,12 @@ Implement the Minimum Viable Product for the multimodal trip planning service, f
 - [x] Run tests - must pass before task 6
 
 ### Task 6: Implement cron job for station status detection
-- [ ] Create `cmd/cron/station_status.go` daily cron job
-- [ ] Query `/schedule` for each monitored station, count flights on upcoming dates
-- [ ] Implement closure detection: N consecutive days of zero trips (N=3 recommended) → status `closed`
-- [ ] Implement reactivation: status `active` when >0 trips appear
-- [ ] Write tests for cron logic (status transition, zero-flight detection, reactivation)
-- [ ] Run tests - must pass before task 7
+- [x] Create `cmd/cron/station_status.go` daily cron job
+- [x] Query `/schedule` for each monitored station, count flights on upcoming dates
+- [x] Implement closure detection: N consecutive days of zero trips (N=3 recommended) → status `closed`
+- [x] Implement reactivation: status `active` when >0 trips appear
+- [x] Write tests for cron logic (status transition, zero-flight detection, reactivation)
+- [x] Run tests - must pass before task 7
 
 ### Task 7: End-to-end integration and full test suite
 - [ ] Write integration tests connecting all components: API → cache → routing → Yandex client