Add an explicit Stop / pause /Abort Scan UI control. #385

Part of #373 Queue Management & Experiment Control:

Build a direct, fail-safe mechanism in the UI to instantly stop/pause and resume an active scan, replacing the current "wait for the scan to finish or the cow to come home method"

Goals

Acceptance criteria : What journeys should the user be able to complete to consider your feature done
Be as specific as you can, check them off once they work. Add more if you find more requirements during development. Issue should only be considered done after all of them are checked

• On-Demand Interruption: The user can safely halt active executions instantly with a single button click.

Tasks

base on the goals, deduce the tasks required. check them off once they're done

• Emergency Stop Button: Add a prominent, highly accessible "Stop / Abort" control in the execution dashboard.
• Pause and resume Button: Add a Pause, Resume abort control in the execution dashboard.