Restore smart screenshot selection

[ryanrhughes]

Summary

• make the default and smart target infer the capture from the gesture: drag for a region, click a window, or click open monitor space for fullscreen
• light exactly the target that will be captured and repair hover damage around antialiased window borders
• remove the capture-kind tab strip and Space-key mode cycling while retaining explicit CLI modes and scrolling capture entry points
• update the README and smoke coverage for the inferred selection flow

Context

This restores the magic selection behavior used by Omarchy's previous screenshot flow. Users no longer need to choose region, window, or fullscreen before interacting with the overlay.

Testing

• make check