Take the icon square up to the touch target, and let it fill the row

Asked for: more space between the header icons, and a box tall enough to
fill the header rather than sitting inside it. 48dp does both -- the marks
stand 31dp apart and 31dp from the screen edge, measured on the emulator,
where the 40dp square had them 23dp apart and 27dp from it.

It is also the platform's minimum touch target, which the previous size
was short of, and it is taller than any header's text: the session
header's row now takes its height from the button and needs no vertical
padding of its own, for the same reason the rows add no gap between two
buttons. The ring around the mark is still the only spacing rule; every
number here moved because it did.

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

app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt

@@ -1309,7 +1309,7 @@ fun SessionScreen(settings: ServerSettings, summary: SessionSummary, onBack: ()
     Column(Modifier.fillMaxSize()) {
         Row(
             verticalAlignment = Alignment.CenterVertically,
-            modifier = Modifier.fillMaxWidth().padding(horizontal = 16.dp, vertical = 4.dp),
+            modifier = Modifier.fillMaxWidth().padding(horizontal = 16.dp),
         ) {
             GlyphButton(BACK_GLYPH, "Back", onBack)
             // A ring's worth, which is what the arrow already keeps on its other three sides --