fix: let the settings panel use the width of the page

Looked at on a 1440px screen it was the one block on the page not using
the column it sits in. The rows were held to max-w-3xl inside an 1150px
shell, but the section's own rule spans the shell — so every hairline
inside the panel stopped a third of the column short of the one above it,
between a two-column checklist and a three-column footer that both go
full width. The measure was there to keep a name and its state reading as
one line, but that pairing is what "running now" already does with a
title and its countdown directly above, so full width is the house
pattern rather than a stretch. Prose inside a group keeps its measure.

The game list was the worse half: eighteen rows of four controls at
max-w-md is a thousand pixels of ribbon down the left with two thirds of
the screen empty beside it. It takes two columns past lg once there are
nine or more games, flowing down then across so the numbers still read in
a straight line and an arrow still swaps a row with its neighbour. Below
nine, and on a phone, it is unchanged.

The last group also loses its bottom rule, which was a second hairline a
few pixels above the footer's own.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

src/client/styles.css

@@ -448,6 +448,15 @@ body {
   border-radius: 3px;
 }
 
+/*
+ * The last group closes the list, so its rule would be a second hairline a few
+ * pixels above the footer's own — two parallel lines with nothing between them,
+ * which reads as a mistake rather than as a boundary.
+ */
+.settings-group:last-child {
+  border-bottom-width: 0;
+}
+
 .settings-chevron {
   transition: transform 150ms ease;
 }