mask_canvas.py:
- Redo stack: new strokes clear it, undo pushes onto it, redo pops from it.
- undo10(): undoes up to 10 steps in one call with a single redraw.
- Brush circle preview: white Circle patch tracks mouse position and shows
current brush radius; hidden when cursor leaves the axes.
- toggle_mask() / btn_mask: hides or shows the green mask overlay without
affecting the underlying mask data.
annotator.py:
- Removed Reload Saved button and reload_saved() — clip already loads its
saved state on navigation, making the button redundant.
- Added Undo×10 and Redo buttons wired to mc.undo10 / mc.redo.
- Added Hide Mask button (mc.btn_mask) to the toolbar row.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
