feat(KB-180): rename pause button titles from 'AI engine' to 'scheduling'

- Update Header pause button titles to 'Pause scheduling' / 'Resume scheduling'
- Update Header unit tests to assert new title strings
- Update App integration tests for engine pause flows to use new titles

packages/dashboard/app/components/Header.tsx

@@ -27,7 +27,7 @@ export function Header({
         <button
           className={`btn-icon${enginePaused ? " btn-icon--paused" : ""}`}
           onClick={onToggleEnginePause}
-          title={enginePaused ? "Resume AI engine" : "Pause AI engine"}
+          title={enginePaused ? "Resume scheduling" : "Pause scheduling"}
           disabled={!!globalPaused}
         >
           {enginePaused ? <Play size={16} /> : <Pause size={16} />}