Add draw-to-create shapes + freehand paint to the Inverse FFT tab

[jacobson30-bot]

Summary

Replaces the Inverse FFT tab's "Add circle / Add ellipse" buttons with three draw-on-canvas tools:

• Ellipse and Rectangle — drag on the FFT to draw; hold Shift for a circle/square (matching normal ROI behaviour). Drawn shapes keep move/resize handles for fine-tuning.
• Paint — freehand brush (brush-size spinbox + color picker) that highlights an irregular Fourier region as a colored transparent overlay.

All three grab their conjugate partner (point reflection through DC) so the reconstruction stays real, and honour the existing Mask controls (Remove/Keep, Conjugate symmetry, Soft edge).

Changes

• inverse_fft.py — FourierRect/FourierStrokes dataclasses, generalized fourier_region_mask (signed-distance rect, disc-union strokes, soft edges), fourier_region_from_dict; fourier_ellipse_mask kept as a back-compat wrapper.
• fft_selection.py — draw-to-create flow with Shift constraint, rectangle patches, q-space-aligned AxesImage paint overlay, handle editing, to_regions().
• fft_viewer_reconstruct_mixin.py — checkable tool buttons (reusing ellipse.png/rectangle.png/freehand.png), brush size + color controls, region-based mask wiring, JSON-safe op params.
• state.py — replay of all region kinds; paint persists as a compact q-space stroke list. Back-compatible with legacy ellipse-only saved states.

Testing

• Full suite: 2089 passed, 3 skipped.
• Extended test_inverse_fft.py (rect/strokes/soft-edge/conjugate/region_from_dict/mixed) and rewrote test_fft_selection_gui.py for the draw/paint interaction.
• Physics review confirmed mask(-q)=mask(q) holds for all region kinds; state replay matches the in-viewer preview exactly.

🤖 Generated with Claude Code