Show selection origin coordinates in status bar

[vrnvorona]

Summary

• Display the top-left corner coordinates (X, Y) of the selection alongside its dimensions (W × H) in the status bar
• Format: X, Y | W × H — makes it easy to read both position and size at a glance
• Label is cleared when no selection is active instead of showing 0, 0

Test plan

• Create a rectangular selection and verify the status bar shows X, Y | W × H
• Move/resize the selection and confirm coordinates update correctly
• Deselect all and verify the label is cleared
• Test with selections near canvas edges and large coordinates

🤖 Generated with Claude Code

[vrnvorona]

Initial:
Move:
Clear:

Full canvas:

Change is simple. Empty is also 0,0 as it should be.

Just in case: I am sorry-ish for blatant AI usage, but I am so used to Paint.NET having this feature and hope it's good addition to repo.

[vrnvorona]

@cameronwhite CC as I can't asign reviewers.

[cameronwhite]

Could you file this as an issue instead please?
I think it's a good idea, but needs more design discussion to avoid taking up so much horizontal space which we may want for other purposes (also related to issue #1362). I'm also unlikely to merge entirely AI-generated contributions