[FEATURE] picker: highlight the selected code block in the response

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When using /copy with multiple code blocks, the picker only shows the first line of each block (e.g. import
  Foundation, func createPost...).

  It's very difficult to tell which picker item corresponds to which code block in the response — especially when
  multiple blocks start with similar lines. I have to scroll back up and mentally count "this is the 2nd code block"
  to figure out what I'm copying.

Proposed Solution

When navigating the /copy picker with arrow keys, visually highlight the corresponding code block in the response
  above, and dim the rest of the response.

  As the user moves up/down in the picker, the highlight follows to the matching block. This gives immediate visual
  feedback about the exact copy range.

Alternative Solutions

Currently I work around this by selecting "Full response" and manually finding the code block I need after pasting.
  Or I scroll back up and count code blocks to match the picker number.

Priority

Low - Nice to have

Feature Category

CLI commands and flags

Use Case Example

1. I ask Claude to generate code, and it responds with 3+ code blocks (e.g. Model, ViewModel, View)
2. I run /copy to copy just the ViewModel code
3. The picker shows: "import Foundation" (29 lines), "func createPost..." (24 lines), "import SwiftUI" (23 lines)
4. Multiple blocks start with similar imports — I can't tell which is which
5. With this feature, I could see the actual block highlighted in the response above as I navigate the picker, and

  confidently select the right one

Additional Context

This is especially problematic when Claude generates multiple Swift files in one response, as many blocks start with
   the same import statements (import Foundation, import SwiftUI, etc.).