fix(ui): give the Settings Theme row back its top gap

The Application section stacks its rows with rowOverlap(), a negative
spacing that trades away one label's duplicated text inset. The Theme
row's value is a Select, which paints its box out to the row's edge and
has no inset to give, so the overlap closed the gap instead: 0.46 px
between the Notifications checkbox and the dropdown, against ~8 px
between the checkbox rows.

cancelRowOverlap adds that one padding back on the Theme row's top edge
only, restoring the gap to 7.5 px without touching the other rows or the
column width.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/CHANGELOG.md

@@ -46,6 +46,11 @@ dragged.**
 - The **Application** and **About** blocks are about 2 px tighter: every stacked
   row group in the app now shares one spacing derived from the theme rather than
   three separately tuned numbers.
+- The **Theme** dropdown is no longer flush against the **Notifications**
+  checkbox. That shared row spacing pulls rows together by one text inset, which
+  the rows above have to give but a dropdown — which paints its box out to the
+  row's edge — does not, so the gap collapsed to about a pixel. The Theme row
+  now keeps the same gap the checkbox rows have.
 
 ## 0.15.0 - 2026-07-26