feat: Add border styling to input field

- Add single-line gray border around input field
- Apply horizontal padding only for compact appearance
- Improve visual separation of input area

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: koki-develop

src/components/InputField.tsx

@@ -16,7 +16,7 @@ export const InputField: React.FC<InputFieldProps> = ({
   showCursor,
 }) => {
   return (
-    <Box>
+    <Box borderStyle="single" borderColor="gray" paddingX={1}>
       <Text color="yellow">&gt; </Text>
       <TextInput
         value={value}