Bug: rtk rewrite breaks 2>&1 shell redirection

## Description

`rtk rewrite` inserts spaces into `2>&1`, breaking shell redirection.

## Reproduction

```bash
rtk rewrite "cargo test 2>&1 | head"
# Output: rtk cargo test 2> & 1 | head
# Expected: rtk cargo test 2>&1 | head
```

## Impact

Any command using `2>&1` piped to another command gets broken silently. The rewritten command will fail or behave unexpectedly.