Phase 006 Execution

Scope

Added maintenance schedule management pages.
Added manual schedule baselines for mileage and time calculations.
Added overdue, upcoming, no-history, and current maintenance status calculations.
Added vehicle show alerts for overdue, upcoming, and no-history schedules.
Added logger-backed notification behavior for status changes.
Added specs for schedule CRUD and maintenance status behavior.

Added schedule fields for baseline_odometer, baseline_date, active, last_status, and last_status_changed_at.
Added validation for manual baselines and schedule active state.
Added nested maintenance schedule routes under vehicles.
Added MaintenanceSchedulesController with list, show, new, create, edit, update, and deactivate actions.
Added separate maintenance schedule views and a shared form partial.
Added MaintenanceScheduleStatus for calculating due odometer/date and status.
Added MaintenanceNotification as the isolated notification stub that logs status changes through Rails.logger.
Updated vehicles#show to show overdue alerts, upcoming warnings, no-history notices, next due odometer, next due date, and status.
Updated maintenance entry validation and forms to use only active schedules for new entries.
Added request specs for schedule CRUD, soft deactivation, vehicle alerts, and status-change logging.
Added model specs for mileage-based, time-based, upcoming, no-history, and current status cases.

Maintenance schedule baselines are manually entered per schedule.
Without matching maintenance history, status uses the schedule baseline.
With matching maintenance history, status uses the latest matching maintenance entry instead of the schedule baseline.
A schedule is overdue exactly when either mileage or time interval is reached.
Upcoming warnings use a 5% lead window for both mileage and time intervals.
Schedules are soft-deactivated instead of deleted.
Vehicle show is allowed to update stored status tracking and log status changes.
Status changes are stored for all statuses, but notifications are logged only for upcoming and overdue statuses.

Passed: bundle exec rspec spec/models/maintenance_schedule_spec.rb spec/models/maintenance_schedule_status_spec.rb
Passed: bundle exec rspec spec/requests/vehicles_spec.rb
Passed: bundle exec rspec
Passed: bin/rubocop app/models/maintenance_schedule.rb app/models/maintenance_entry.rb app/models/maintenance_schedule_status.rb app/models/maintenance_notification.rb app/controllers/vehicles_controller.rb app/controllers/fuel_entries_controller.rb app/controllers/maintenance_entries_controller.rb app/controllers/maintenance_schedules_controller.rb spec/models/maintenance_schedule_spec.rb spec/models/maintenance_schedule_status_spec.rb spec/requests/vehicles_spec.rb
Passed: bin/ci