frontend: require local arming before motor tests

[Daniiiil1]

Summary

• track whether the PWM setup page successfully armed the vehicle
• send MAV_CMD_DO_MOTOR_TEST only while that page owns the arming state
• keep motor controls disabled and explain the state when the vehicle was armed elsewhere
• clear ownership whenever the vehicle disarms or this page requests disarming

This prevents opening PWM Outputs on an already-armed vehicle from immediately starting the periodic motor-test command loop.

Closes #3545

Validation

• yarn eslint --max-warnings=0 --ext .vue --ignore-path .gitignore src/components/vehiclesetup/PwmSetup.vue
• yarn stylelint src/components/vehiclesetup/PwmSetup.vue
• yarn build
• git diff --check

The repository pre-push hook could not start because Docker is unavailable in this local macOS environment. No hardware test was performed.