fix(app): balance composer right-side button spacing

Tightens transparent icon gaps to 4px and gives filled action buttons
(send, interrupt) a 4px left margin so they sit 8px from neighbors.
Shrinks context-window meter SVG from 20 to 16 to match the visual
weight of surrounding icons.

packages/app/src/components/message-input.tsx

@@ -1365,7 +1365,7 @@ const styles = StyleSheet.create(((theme: any) => ({
     flexShrink: 0,
     flexDirection: "row",
     alignItems: "center",
-    gap: isWeb ? theme.spacing[2] : theme.spacing[1],
+    gap: theme.spacing[1],
   },
   attachButton: {
     width: 28,
@@ -1399,6 +1399,7 @@ const styles = StyleSheet.create(((theme: any) => ({
     backgroundColor: theme.colors.accent,
     alignItems: "center",
     justifyContent: "center",
+    marginLeft: theme.spacing[1],
   },
   iconButtonHovered: {
     backgroundColor: theme.colors.surface2,