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/composer.tsx

@@ -840,11 +840,12 @@ const styles = StyleSheet.create(((theme: Theme) => ({
     backgroundColor: theme.colors.palette.red[600],
     alignItems: "center",
     justifyContent: "center",
+    marginLeft: theme.spacing[1],
   },
   rightControls: {
     flexDirection: "row",
     alignItems: "center",
-    gap: theme.spacing[2],
+    gap: theme.spacing[1],
   },
   contextWindowMeterSlot: {
     width: 28,