ui: split Settings into General / Global gaming / Windows services / Display tabs

Single-window scroll was getting unwieldy with the services section added.
Each tab now has its own ScrollViewer; the Cancel/Apply/Save row stays
docked at the bottom across all tabs. Bumped default width 780 -> 820 so
tab headers fit comfortably; reduced default height 760 -> 720 since
each tab needs less vertical space than the combined view. All x:Names,
bindings, and event handlers preserved unchanged — code-behind didn't
need to change.

Author: carterscode