fix(companion): move ad-hoc dashboard impl into private/openAdHocPlot.m

Previous commit added the new DashboardEngine-based impl at
libs/FastSenseCompanion/openAdHocPlot.m, but MATLAB's private-folder
rules mean the orchestrator (which lives in libs/FastSenseCompanion/)
resolves the call to the old private/openAdHocPlot.m first — so the
new code path was never executed.

Moves the new content into private/openAdHocPlot.m (overwriting the
old classical-figure impl) and removes the misplaced public copy.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: HanSur94