feat(ui): standardize semantic focus colors and enhance history visibility (#20745)

Co-authored-by: jacob314 <jacob314@gmail.com>

packages/cli/src/ui/components/SessionBrowser.tsx

@@ -7,6 +7,7 @@
 import type React from 'react';
 import { useState, useCallback, useMemo, useEffect, useRef } from 'react';
 import { Box, Text } from 'ink';
+import { theme } from '../semantic-colors.js';
 import { Colors } from '../colors.js';
 import { useTerminalSize } from '../hooks/useTerminalSize.js';
 import { useKeypress } from '../hooks/useKeypress.js';
@@ -436,7 +437,7 @@ const SessionItem = ({
     if (isDisabled) {
       return Colors.Gray;
     }
-    return isActive ? Colors.AccentPurple : c;
+    return isActive ? theme.ui.focus : c;
   };
 
   const prefix = isActive ? '❯ ' : '  ';
@@ -483,7 +484,10 @@ const SessionItem = ({
     ));
 
   return (
-    <Box flexDirection="row">
+    <Box
+      flexDirection="row"
+      backgroundColor={isActive ? theme.background.focus : undefined}
+    >
       <Text color={textColor()} dimColor={isDisabled}>
         {prefix}
       </Text>