refactor(displays): move overlay placement geometry onto the alignment

[esphynox]

Summary

Fixes issue (#103)

• Move keyboard overlay placement geometry onto the alignment model so preview positioning and live placement use the same source of truth.
• Keep custom placement anchored to the selected preview point instead of recalculating from separate window geometry.
• Add focused placement and normalized-point tests to cover the new alignment behavior.

Tests

• tuist generate
• xcodebuild test -project Keyty.xcodeproj -scheme Keyty -destination 'platform=macOS'
• Other:

Run project commands from Apps/Keyty.

UI Changes

Attach screenshots or screen recordings for visible UI changes. Write N/A if there are none.

Before	After
keyty-custom-alignment-before.mov	keyty-custom-alignment-after.mov

Documentation

• Updated relevant docs
• No docs needed

Release Notes

Improve keyboard overlay custom placement so the overlay stays aligned to the selected anchor in display previews and live placement.