Add full-height vertical eighth window actions

[Soren90912]

Summary

Adds 8 new full-height vertical eighth window actions for wide and ultrawide displays.

Each action places the window into one of eight equal-width columns across the usable screen area:

• First Vertical Eighth
• Second Vertical Eighth
• Third Vertical Eighth
• Fourth Vertical Eighth
• Fifth Vertical Eighth
• Sixth Vertical Eighth
• Seventh Vertical Eighth
• Last Vertical Eighth

The existing 4x2 eighth actions and their identifiers remain unchanged.

Implementation

• Added 8 new WindowAction cases with stable identifiers.
• Added a shared VerticalEighthCalculation.
• Uses the current screen's adjusted visible frame.
• Handles widths that are not evenly divisible by 8 without cumulative gaps or overlap.
• Supports Rectangle's existing gap behavior.
• Added shortcut preference rows and icons.
• Added English and Traditional Chinese localization.
• Works across multiple displays.

Screenshots

Shortcut preferences

Vertical eighth placement

Validation

• 344 tests passed.
• Debug build passed.
• Release build passed.
• Manual smoke test passed:
  • shortcut configuration
  • first / second vertical eighth placement
  • rightmost eighth boundary
  • gap behavior
  • second display
• Existing 4x2 eighth behavior remains unchanged.

[rxhanson]

Thanks for contributing. Typically I would suggest moving these into the Extras button popover in the General tab, but I'm in the middle of converting the shortcuts settings tab into an outline view to accommodate more sizes. Seeing as there's already a merge conflict on this PR, perhaps the best path forward is to hold off on making more changes until the outline view is in place? The alternative would be to simply pull out the Storyboard changes for now and fix the merge conflict and I can add them back into the outline view when it's ready.