add: mask drawing tools (brush/rectangle/line), undo/redo, and edit mode

[Osayi-ANL]

Adds interactive mask editing to the mask viewer: brush, rectangle, and line
tools with undo/redo, an edit mode toggle, and orientation-aware display so
the mask lines up with the diffraction image regardless of transpose/rotate
state.

• Brush/Rectangle/Line tools, undo/redo, and edit mode in the mask editor
• Edit Mask button replaces Show Mask; opens the editor with a blank mask if none is loaded
• Clamp mask-editor strokes to the image bounds so drawing past an edge fills up to it instead of the shape vanishing
• Full redraw (not just the overlay) after undo/redo across a transpose or rotate, so the mask doesn't render stretched
• Prompt to save or discard changes when closing the mask editor

Test Plan

• Open area detector viewer and click edit mask -- try the functionality

[pecomyint]

Nice feature — the paint helpers are clean and detector-agnostic, the commits are well-split, and ruff passes. The separate red ImageItem overlay is the right call for cheap live drawing.

Blockers

1. Close prompt's "Save" doesn't save (mask_viewer.py:219-232). QMessageBox.Save is the default button and falls through to event.accept() — _save_mask() is never called. Harmless today only because _on_mask_edited saves on every emit.
2. Save button then close still prompts "unsaved changes" — _save_mask (:460-476) never refreshes self._original_mask. One line.
3. _display_to_native is now in the mouse-move path (:330-350). The probe-array + np.argwhere reverse-map costs 9 ms/call on a 2048² mask, and _event_native now calls it on every move during a drag — ~12 ms/move for the brush, ~28 ms for a long line preview, scaling to 50-110 ms on a 4096² detector (visible lag, skipped pixels). transpose+rot90 is a closed-form index permutation, so this can be pure arithmetic instead of building and scanning an array. Hoisting the three _get_display_mask() copies and the per-move np.sum picks up the rest.

Worth fixing here

4. "Size" means different things per tool — at 3, brush paints 5 px but rectangle and line paint 3 px. _paint_disk reads the value as a radius (diameter 2R-1); _paint_line already compensates with (thickness + 1) / 2, the brush should too.
5. Opening the editor writes to disk — edit_mask_clicked (area_det_viewer.py:718-731) creates an all-False mask and immediately saves it, so just opening the window flips mask_manager.mask off None and the user needs "Clear Mask" to undo it. Can the create+save wait for the first real edit?

Minor: _get_parent_display_settings's colormap return is now dead (:410); the Redo tooltip says Ctrl+Y but QKeySequence.Redo is Cmd+Shift+Z on macOS; MASK_UNDO_MAX = 20 bounds snapshot count, not bytes (~360 MB on an Eiger 16M) despite the comment. The paint helpers fit the fake-self pattern in tests/unit/test_roi_visibility.py — cheap tests there would lock in 3 and 4.