Add move window to specific display by number

[LucasZdv]

Summary

Adds support for moving the focused window directly to a specific display (1–9) using keyboard shortcuts, instead of cycling through displays sequentially with Next/Previous Display.

This addresses the feature requested in #199, which was closed without the specific-display-by-number functionality being implemented.

• New WindowAction cases: displayOne through displayNine
• New SpecificDisplayCalculation class (modeled after NextPrevDisplayCalculation)
• Screens are sorted by x-coordinate (left to right); if the target display is not connected, the action is silently ignored
• Shortcuts are configurable via Terminal commands (no UI changes), as suggested by @rxhanson in Move window to an specific Display #199

Configuration example

defaults write com.knollsoft.Rectangle displayOne -dict-add keyCode -float 18 modifierFlags -float 1835305
defaults write com.knollsoft.Rectangle displayTwo -dict-add keyCode -float 19 modifierFlags -float 1835305

Motivation

As a user with 4+ monitors, cycling through displays with Next/Previous is inefficient. This feature allows jumping directly to any display by number, which is significantly faster in multi-monitor setups.

I am also a Rectangle Pro license holder and would love to see this feature included in Pro as well.

Test plan

• Tested with 4 displays on macOS
• Verified shortcuts work correctly (window moves to the expected display)
• Verified that targeting a disconnected display is handled gracefully (no-op)
• Verified that attemptMatchOnNextPrevDisplay setting is respected

[rxhanson]

Thanks for contributing! Looks good.

This is actually configurable in Rectangle Pro using the Custom Size & Position functionality, but it makes sense to have this rolled in there as well.