fix(ui): stop resetting window size on every activation

[obesity40]

Fixes a bug where resizing a window was undone as soon as it regained focus.

Repro

1. Open Settings (or any OddSnap window).
2. Resize it — e.g. drag the bottom edge to make it taller.
3. Click another application, then click back into OddSnap.
4. The window snaps back to its previous size.

Cause

UiScale.ApplyToWindow is called on every Activated event so the palette can
be refreshed. Besides setting the theme, it also re-applies the design-time
window bounds from the recorded WindowScaleState, which overwrites whatever
size the user just chose.

Fix

Track the scale that was last applied and return early when it has not changed,
so the bounds are only written when the UI scale itself changes:

if (Math.Abs(state.LastAppliedScale - scale) < 0.001)
    return;

state.LastAppliedScale = scale;