feat: Display image and crop dimensions in toolbar

[prime-run]

This PR adds image and crop dimensions display to the toolbar for better visibility and fixed-size rendering.

• Show full image dimensions in toolbar (bottom right) when crop tool is inactive
• Display crop selection dimensions when crop tool is active

NOTE: event flow from CropTool → SketchBoard → App → StyleToolbar

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Update: eab8720 Adds:

• Esc key cancels crop selection instead of killing process when crop tool is active.

[RobertMueller2]

Thank you for your contribution. It might take a few days to review.

[RobertMueller2]

Ok, I've had a look. Few small things I'd like to see changed within the PR:

• I think the tooltip should say "Output dimensions (width x height)". This makes sense regardless of whether there is any crop or not.
• When exiting the crop tool (e.g. by clicking Pointer), the displayed dimension reverts to the original image size. It should only revert if crop selection is removed entirely (esc)
• The toolbar size can change when e.g. the displayed dimensions jump from e.g. "600x400" to "5x10" due to creating a new crop rectangle. Obviously we can't account for everything, but a minimum size of the control that accommodates XXXXxYYYY would be good. set_width_chars should be possible, I think, but haven't tried it.

Additional remarks regarding the crop tool for future discussion:

• I'm finding it a bit counter-intuitive that there's a key to remove crop selection entirely (esc) but none to finish editing it. This may need some additional usability discussion which I'll open an issue for. (edit: Crop usability improvements after PR #357 #364)
• Our minimum width is too narrow now, although that was true before this change and worse for the top toolbar than the bottom. I'll open an issue to adjust that as well. (edit: Adjust minimum width #365)