Add Layout Helper and shared window dividers + a few optimizations

[kiteretsu903]

1. Layout Helper: I added a chooser to fill the remaining space after snapping. Escape or a click outside dismisses it.

2. Shared dividers: I added dragging to resize adjacent left/right or top/bottom windows together. Double-click restores an equal split.

3. Fit remaining space: added an option to snap beside an existing window without resizing it.

4. Defaults and permissions: These features are off by default. Thumbnails require Screen Recording access on macOS 14 or later. Without Screen Recording, it still shows icons and titles.

5. Minimum sizes: shorten warning size + an option to turn it on/off. Also added "learned size limits", which help with later snaps, previews, and divider dragging, and can be inspected, cleared, or saved across restarts. Reaching a minimum size still allows placement.

6. Optimizations & fixes

• Window animations: adjusted animation timing to account for how quickly each app responds to resize requests, reducing repeated writes and last-second corrections.
• Non-animate window moving path optimization: reduced redundant resize calls and choose whether to resize or move first based on the window’s position and screen boundaries.
• Preview animations: moved Snap Preview transitions and divider fades to Core Animation, reducing per-frame work on the main thread.
• UX optimization for blur preview + animate window combination: show the preview behind the moving window so it stays visible throughout the snap animation. This is a more natural user experience: with window animations on, the window moves visibly over the preview; however with animations off, the preview stays in front to soften the abrupt resize.

[rxhanson]

Great, these look like nice additions.

I'm getting ready to merge in an overhaul of the settings window, and draft a release this week. Since this is a pretty large change, my plan is to do that prior to reviewing this PR, and just a heads up that I was also planning on adding at least the toggle for being able to turn off the "minimum window size reached" notification.

[kiteretsu903]

@rxhanson sounds good to me!