feat: add interactive band cutting to region capture

[devmobasa]

Summary

Adds an interactive Cut mode to region capture Review.

Users can remove unwanted horizontal or vertical bands from a capture before copying, saving, or sending it to the Board. This is useful for collapsing irrelevant sections in code, conversations, documents, and long screenshots.

What changed

• Add a Cut button and X shortcut in region Review.
• Drag across the capture to remove a row or column band.
• Support multiple cuts against the already-collapsed result.
• Add undo, redo, and reset controls.
• Keep raw and annotated exports geometrically identical.
• Deliver the collapsed output correctly through Copy, Save, Both, and Board.
• Support pointer, touch, stylus, and keyboard input.
• Lock crop adjustments while cuts exist.
• Add asynchronous preview rendering with stale-result rejection and visible failure handling.
• Avoid copying the full raster when the cut stack is empty.

Implementation notes

• Band-cut geometry and pixel composition are isolated in capture::band_cut.
• Review edits are transient and initialized whenever a selection enters Review.
• Preview jobs use revision and source correlation to reject obsolete results.
• Unedited previews reuse their existing shared raster.
• Source changes cancel Review, while recoverable preview failures keep Review active.